I have a pretty simple script that is something like the following:
#!/bin/bash
VAR1="$1"
MOREF='sudo run command against $VAR1 | grep name | cut -c7-'
echo $MOREF
When I run this script from the command line and pass it the arguments, I am not getting any output. However, when I run the commands contained within the $MOREF variable, I am able to get output.
How can one take the results of a command that needs to be run within a script, save it to a variable, and then output that variable on the screen?
In addition to backticks `command`, command substitution can be done with $(command) or "$(command)", which I find easier to read, and allows for nesting.
OUTPUT=$(ls -1)
echo "${OUTPUT}"
MULTILINE=$(ls \
-1)
echo "${MULTILINE}"
Quoting (") does matter to preserve multi-line variable values; it is optional on the right-hand side of an assignment, as word splitting is not performed, so OUTPUT=$(ls -1) would work fine.
$(sudo run command)
If you're going to use an apostrophe, you need `, not '. This character is called "backticks" (or "grave accent"):
#!/bin/bash
VAR1="$1"
VAR2="$2"
MOREF=`sudo run command against "$VAR1" | grep name | cut -c7-`
echo "$MOREF"
Some Bash tricks I use to set variables from commands
Sorry, there is a loong answer, but as bash is a shell, where the main goal is to run other unix commands and react on result code and/or output, ( commands are often piped filter, etc... ).
Storing command output in variables is something basic and fundamental.
Therefore, depending on
compatibility (posix)
kind of output (filter(s))
number of variable to set (split or interpret)
execution time (monitoring)
error trapping
repeatability of request (see long running background process, further)
interactivity (considering user input while reading from another input file descriptor)
do I miss something?
First simple, old (obsolete), and compatible way
myPi=`echo '4*a(1)' | bc -l`
echo $myPi
3.14159265358979323844
Compatible, second way
As nesting could become heavy, parenthesis was implemented for this
myPi=$(bc -l <<<'4*a(1)')
Using backticks in script is to be avoided today.
Nested sample:
SysStarted=$(date -d "$(ps ho lstart 1)" +%s)
echo $SysStarted
1480656334
bash features
Reading more than one variable (with Bashisms)
df -k /
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/dm-0 999320 529020 401488 57% /
If I just want a used value:
array=($(df -k /))
you could see an array variable:
declare -p array
declare -a array='([0]="Filesystem" [1]="1K-blocks" [2]="Used" [3]="Available" [
4]="Use%" [5]="Mounted" [6]="on" [7]="/dev/dm-0" [8]="999320" [9]="529020" [10]=
"401488" [11]="57%" [12]="/")'
Then:
echo ${array[9]}
529020
But I often use this:
{ read -r _;read -r filesystem size using avail prct mountpoint ; } < <(df -k /)
echo $using
529020
( The first read _ will just drop header line. ) Here, in only one command, you will populate 6 different variables (shown by alphabetical order):
declare -p avail filesystem mountpoint prct size using
declare -- avail="401488"
declare -- filesystem="/dev/dm-0"
declare -- mountpoint="/"
declare -- prct="57%"
declare -- size="999320"
declare -- using="529020"
Or
{ read -a head;varnames=(${head[#]//[K1% -]});varnames=(${head[#]//[K1% -]});
read ${varnames[#],,} ; } < <(LANG=C df -k /)
Then:
declare -p varnames ${varnames[#],,}
declare -a varnames=([0]="Filesystem" [1]="blocks" [2]="Used" [3]="Available" [4]="Use" [5]="Mounted" [6]="on")
declare -- filesystem="/dev/dm-0"
declare -- blocks="999320"
declare -- used="529020"
declare -- available="401488"
declare -- use="57%"
declare -- mounted="/"
declare -- on=""
Or even:
{ read _ ; read filesystem dsk[{6,2,9}] prct mountpoint ; } < <(df -k /)
declare -p mountpoint dsk
declare -- mountpoint="/"
declare -a dsk=([2]="529020" [6]="999320" [9]="401488")
(Note Used and Blocks is switched there: read ... dsk[6] dsk[2] dsk[9] ...)
... will work with associative arrays too: read _ disk[total] disk[used] ...
Other related sample: Parsing xrandr output: and end of Firefox tab by bash in a size of x% of display size? or at AskUbuntu.com Parsing xrandr output
Dedicated fd using unnamed fifo:
There is an elegent way! In this sample, I will read /etc/passwd file:
users=()
while IFS=: read -u $list user pass uid gid name home bin ;do
((uid>=500)) &&
printf -v users[uid] "%11d %7d %-20s %s\n" $uid $gid $user $home
done {list}</etc/passwd
Using this way (... read -u $list; ... {list}<inputfile) leave STDIN free for other purposes, like user interaction.
Then
echo -n "${users[#]}"
1000 1000 user /home/user
...
65534 65534 nobody /nonexistent
and
echo ${!users[#]}
1000 ... 65534
echo -n "${users[1000]}"
1000 1000 user /home/user
This could be used with static files or even /dev/tcp/xx.xx.xx.xx/yyy with x for ip address or hostname and y for port number or with the output of a command:
{
read -u $list -a head # read header in array `head`
varnames=(${head[#]//[K1% -]}) # drop illegal chars for variable names
while read -u $list ${varnames[#],,} ;do
((pct=available*100/(available+used),pct<10)) &&
printf "WARN: FS: %-20s on %-14s %3d <10 (Total: %11u, Use: %7s)\n" \
"${filesystem#*/mapper/}" "$mounted" $pct $blocks "$use"
done
} {list}< <(LANG=C df -k)
And of course with inline documents:
while IFS=\; read -u $list -a myvar ;do
echo ${myvar[2]}
done {list}<<"eof"
foo;bar;baz
alice;bob;charlie
$cherry;$strawberry;$memberberries
eof
Practical sample parsing CSV files:
As this answer is loong enough, for this paragraph,
I just will let you refer to
this answer to How to parse a CSV file in Bash?, I read a file by using an unnamed fifo, using syntax like:
exec {FD}<"$file" # open unnamed fifo for read
IFS=';' read -ru $FD -a headline
while IFS=';' read -ru $FD -a row ;do ...
... But using bash loadable CSV module.
On my website, you may find the same script, reading CSV as inline document.
Sample function for populating some variables:
#!/bin/bash
declare free=0 total=0 used=0 mpnt='??'
getDiskStat() {
{
read _
read _ total used free _ mpnt
} < <(
df -k ${1:-/}
)
}
getDiskStat $1
echo "$mpnt: Tot:$total, used: $used, free: $free."
Nota: declare line is not required, just for readability.
About sudo cmd | grep ... | cut ...
shell=$(cat /etc/passwd | grep $USER | cut -d : -f 7)
echo $shell
/bin/bash
(Please avoid useless cat! So this is just one fork less:
shell=$(grep $USER </etc/passwd | cut -d : -f 7)
All pipes (|) implies forks. Where another process have to be run, accessing disk, libraries calls and so on.
So using sed for sample, will limit subprocess to only one fork:
shell=$(sed </etc/passwd "s/^$USER:.*://p;d")
echo $shell
And with Bashisms:
But for many actions, mostly on small files, Bash could do the job itself:
while IFS=: read -a line ; do
[ "$line" = "$USER" ] && shell=${line[6]}
done </etc/passwd
echo $shell
/bin/bash
or
while IFS=: read loginname encpass uid gid fullname home shell;do
[ "$loginname" = "$USER" ] && break
done </etc/passwd
echo $shell $loginname ...
Going further about variable splitting...
Have a look at my answer to How do I split a string on a delimiter in Bash?
Alternative: reducing forks by using backgrounded long-running tasks
In order to prevent multiple forks like
myPi=$(bc -l <<<'4*a(1)'
myRay=12
myCirc=$(bc -l <<<" 2 * $myPi * $myRay ")
or
myStarted=$(date -d "$(ps ho lstart 1)" +%s)
mySessStart=$(date -d "$(ps ho lstart $$)" +%s)
This work fine, but running many forks is heavy and slow.
And commands like date and bc could make many operations, line by line!!
See:
bc -l <<<$'3*4\n5*6'
12
30
date -f - +%s < <(ps ho lstart 1 $$)
1516030449
1517853288
So we could use a long running background process to make many jobs, without having to initiate a new fork for each request.
You could have a look how reducing forks make Mandelbrot bash, improve from more than eight hours to less than 5 seconds.
Under bash, there is a built-in function: coproc:
coproc bc -l
echo 4*3 >&${COPROC[1]}
read -u $COPROC answer
echo $answer
12
echo >&${COPROC[1]} 'pi=4*a(1)'
ray=42.0
printf >&${COPROC[1]} '2*pi*%s\n' $ray
read -u $COPROC answer
echo $answer
263.89378290154263202896
printf >&${COPROC[1]} 'pi*%s^2\n' $ray
read -u $COPROC answer
echo $answer
5541.76944093239527260816
As bc is ready, running in background and I/O are ready too, there is no delay, nothing to load, open, close, before or after operation. Only the operation himself! This become a lot quicker than having to fork to bc for each operation!
Border effect: While bc stay running, they will hold all registers, so some variables or functions could be defined at initialisation step, as first write to ${COPROC[1]}, just after starting the task (via coproc).
Into a function newConnector
You may found my newConnector function on GitHub.Com or on my own site (Note on GitHub: there are two files on my site. Function and demo are bundled into one unique file which could be sourced for use or just run for demo.)
Sample:
source shell_connector.sh
tty
/dev/pts/20
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
29019 pts/20 Ss 0:00 bash
30745 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
newConnector /usr/bin/bc "-l" '3*4' 12
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
29019 pts/20 Ss 0:00 bash
30944 pts/20 S 0:00 \_ /usr/bin/bc -l
30952 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
declare -p PI
bash: declare: PI: not found
myBc '4*a(1)' PI
declare -p PI
declare -- PI="3.14159265358979323844"
The function myBc lets you use the background task with simple syntax.
Then for date:
newConnector /bin/date '-f - +%s' #0 0
myDate '2000-01-01'
946681200
myDate "$(ps ho lstart 1)" boottime
myDate now now
read utm idl </proc/uptime
myBc "$now-$boottime" uptime
printf "%s\n" ${utm%%.*} $uptime
42134906
42134906
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
29019 pts/20 Ss 0:00 bash
30944 pts/20 S 0:00 \_ /usr/bin/bc -l
32615 pts/20 S 0:00 \_ /bin/date -f - +%s
3162 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
From there, if you want to end one of background processes, you just have to close its fd:
eval "exec $DATEOUT>&-"
eval "exec $DATEIN>&-"
ps --tty pts/20 fw
PID TTY STAT TIME COMMAND
4936 pts/20 Ss 0:00 bash
5256 pts/20 S 0:00 \_ /usr/bin/bc -l
6358 pts/20 R+ 0:00 \_ ps --tty pts/20 fw
which is not needed, because all fd close when the main process finishes.
As they have already indicated to you, you should use `backticks`.
The alternative proposed $(command) works as well, and it also easier to read, but note that it is valid only with Bash or KornShell (and shells derived from those),
so if your scripts have to be really portable on various Unix systems, you should prefer the old backticks notation.
I know three ways to do it:
Functions are suitable for such tasks:**
func (){
ls -l
}
Invoke it by saying func.
Also another suitable solution could be eval:
var="ls -l"
eval $var
The third one is using variables directly:
var=$(ls -l)
OR
var=`ls -l`
You can get the output of the third solution in a good way:
echo "$var"
And also in a nasty way:
echo $var
Just to be different:
MOREF=$(sudo run command against $VAR1 | grep name | cut -c7-)
When setting a variable make sure you have no spaces before and/or after the = sign. I literally spent an hour trying to figure this out, trying all kinds of solutions! This is not cool.
Correct:
WTFF=`echo "stuff"`
echo "Example: $WTFF"
Will Fail with error "stuff: not found" or similar
WTFF= `echo "stuff"`
echo "Example: $WTFF"
If you want to do it with multiline/multiple command/s then you can do this:
output=$( bash <<EOF
# Multiline/multiple command/s
EOF
)
Or:
output=$(
# Multiline/multiple command/s
)
Example:
#!/bin/bash
output="$( bash <<EOF
echo first
echo second
echo third
EOF
)"
echo "$output"
Output:
first
second
third
Using heredoc, you can simplify things pretty easily by breaking down your long single line code into a multiline one. Another example:
output="$( ssh -p $port $user#$domain <<EOF
# Breakdown your long ssh command into multiline here.
EOF
)"
You need to use either
$(command-here)
or
`command-here`
Example
#!/bin/bash
VAR1="$1"
VAR2="$2"
MOREF="$(sudo run command against "$VAR1" | grep name | cut -c7-)"
echo "$MOREF"
If the command that you are trying to execute fails, it would write the output onto the error stream and would then be printed out to the console.
To avoid it, you must redirect the error stream:
result=$(ls -l something_that_does_not_exist 2>&1)
This is another way and is good to use with some text editors that are unable to correctly highlight every intricate code you create:
read -r -d '' str < <(cat somefile.txt)
echo "${#str}"
echo "$str"
You can use backticks (also known as accent graves) or $().
Like:
OUTPUT=$(x+2);
OUTPUT=`x+2`;
Both have the same effect. But OUTPUT=$(x+2) is more readable and the latest one.
Here are two more ways:
Please keep in mind that space is very important in Bash. So, if you want your command to run, use as is without introducing any more spaces.
The following assigns harshil to L and then prints it
L=$"harshil"
echo "$L"
The following assigns the output of the command tr to L2. tr is being operated on another variable, L1.
L2=$(echo "$L1" | tr [:upper:] [:lower:])
Mac/OSX nowadays come with old Bash versions, ie GNU bash, version 3.2.57(1)-release (arm64-apple-darwin21). In this case, one can use:
new_variable="$(some_command)"
A concrete example:
newvar="$(echo $var | tr -d '123')"
Note the (), instead of the usual {} in Bash 4.
Some may find this useful.
Integer values in variable substitution, where the trick is using $(()) double brackets:
N=3
M=3
COUNT=$N-1
ARR[0]=3
ARR[1]=2
ARR[2]=4
ARR[3]=1
while (( COUNT < ${#ARR[#]} ))
do
ARR[$COUNT]=$((ARR[COUNT]*M))
(( COUNT=$COUNT+$N ))
done
I'm parsing the result of executing this composite command
ntpq -c peers | awk ' $0 ~ /^*/ {print $9}'
in order to obtain the offset of the active ntp server.
This is the java code used and executed periodically
public Double getClockOffset() {
Double localClockOffset = null;
try {
String[] cmd = {"/bin/sh",
"-c",
"ntpq -c peers | awk \' $0 ~ /^\\*/ {print $9}\'"};
Process p = Runtime.getRuntime().exec(cmd);
p.waitFor();
BufferedReader buf = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = buf.readLine();
if (!StringUtils.isEmpty(line)) {
localClockOffset = Double.parseDouble(line.trim());
} else {
// Log "NTP -> Empty line - No active servers - Unsynchronized"
}
} catch (Exception e) {
// Log exception
}
return localClockOffset;
}
ntpq result example
> remote refid st t when poll reach delay offset jitter
> ==============================================================================
> *server001s1 .LOCL. 1 u 33 64 377 0.111 -0.017 0.011
> +server002s1 10.30.10.6 2 u 42 64 377 0.106 -0.006 0.027
> +server003s1 10.30.10.6 2 u 13 64 377 0.120 -0.009 0.016
Notice that awk searchs the first line beginnig with '*' and extracts its ninth column. In the example: -0.017
The problem is that sometimes I'm obtaining the no-active-servers log message - intended to appear when there is no server with '*'- while the execution of the command through the console returns a number.
I know that I'm not closing the BufferedReader in that code but is that the reason of this behaviour? A new instance is being created (and left open until garbage collecting) in each method invocation but I think that it shouldn't be the cause of this problem.
Runtime.exec() simply invokes the ProcessBuilder inside it, like that:
public Process More ...exec(String[] cmdarray, String[] envp, File dir)
throws IOException {
return new ProcessBuilder(cmdarray)
.environment(envp)
.directory(dir)
.start();
}
see OpenJDK Runtime.java
So there is nothing wrong with using it instead of the ProcessBuilder as is.
The problem is that you invoke:
p.waitFor();
before you obtained the InputStream.
Which means that the process will be already terminated, by the time you obtain the InputStream, and the output stream data might be or might not be available to you, depending on the OS buffering implementation nuances and precise timing of the operations.
So, if you move the waitFor() to the bottom, your code should start working more reliably.
Under Linux however you should normally be able to read the remaining data from the PIPE buffer, even after the writing process has ended.
And the UNIXProcess implementation in OpenJDK, actually makes an explicit use of that, and tries to drain the remaining data, once the process has exited, so that file descriptor can be reclaimed:
/** Called by the process reaper thread when the process exits. */
synchronized void processExited() {
synchronized (closeLock) {
try {
InputStream in = this.in;
// this stream is closed if and only if: in == null
if (in != null) {
byte[] stragglers = drainInputStream(in);
in.close();
this.in = (stragglers == null) ?
ProcessBuilder.NullInputStream.INSTANCE :
new ByteArrayInputStream(stragglers);
}
} catch (IOException ignored) {}
}
}
And this seems to work reliable enough, at least in my tests, so it would be nice to know which specific version of Linux|Unix and JRE your are running.
Have you also considered the possibility of an application-level problem ?
I.e. ntpq is not really guaranteed to always return a * row.
So, it would be nice to remove the awk part from your pipe, to see if there will be some output at all the times.
Another thing to note is that if one of your shell pipeline steps fails (e.g. the ntpq itself), you will also get an empty output, so you will have to track the STDERR as well (e.g. by merging it with STDOUT via the ProcessBuilder).
Sidenote
Doing waitFor before you start consuming the data, is a bad idea in any case, as if your external process will produce enough output to fill the pipe buffer, it will just hang waiting for someone to read it, which will never happen, as your Java process will be locked in waitFor at the same time.
As pointed by Andrew Thompson, you shall try ProcessBuilder instead.
String[] cmd = {"/bin/sh",
"-c",
"ntpq -c peers | awk \' $0 ~ /^\\*/ {print $9}\'"};
ProcessBuilder pb = new ProcessBuilder(cmd);
pb.redirectErrorStream(true);
Process proc = pb.start();
BufferedReader buf = new BufferedReader(new
InputStreamReader(proc.getInputStream()));
String line = null;
while ((line = buf.readLine()) != null) {
localClockOffset = Double.parseDouble(line.trim());
break;
}
proc.destroy();
Ref ProcessBuilder
Finally we have found the real problem.
I'm not gonna change the accepted anwser, I think that it's useful too but maybe someone can learn from our experience.
My java program is launched with a shell script. When we execute the script manually, ntpq command is found and invoked successfully. The problem arises when the software is fully deployed. In the final environment we've got a cron scheduled demon that keeps our program alive but PATH established by cron is different from the PATH that our profile has got assigned.
PATH used by cron:
.:/usr/bin:/bin
PATH that we got login for launching the script manually:
/usr/sbin:/usr/bin:/bin:/sbin:/usr/lib:/usr/lib64:/local/users/nor:
/usr/local/bin:/usr/local/lib:.
Usually ntpq is in
/usr/sbin/ntpq
After we found the key of our problem, I search StackOverflow and got this relevant question where the problem is better explained and solved.
How to get CRON to call in the correct PATHs
i try to run ffmpeg out java. here my code:
String[] temp = {"ffmpeg\\ffmpeg.exe","-i","input_track.ac3","-threads","0","-af","volume=volume="0.0"dB","-acodec","pcm_s32le","-ac","6","-ar","48000","-f","wav","-","|","ffmpeg\\fdkaac","--ignorelength","-m","1","-o","ouput_track.aac","-"};
ProcessBuilder pb = new ProcessBuilder(temp);
Process p = pb.start();
int ev = 0;
if (p.waitFor() != 0)
{
ev = p.exitValue();
}
i try the comand at windows cmd, here have a problem with "|" at the ffmpeg command line.
maybe someone say my fould?
best regards
This question is similar to How to make pipes work with Runtime.exec()? ... except that it is for Windows.
The problem is essentially the same: the exec methods don't understand shell syntax such as pipes, input or output direction and so on. The solution is essentially the same too: exec the appropriate shell and get that to handle the shell syntax.
In this case, try something like this:
String[] temp = new String[] {
"cmd", "/c",
"ffmpeg\\ffmpeg.exe -i input_track.ac3 -threads 0 " +
"-af volume=volume=\"0.0\"dB -acodec pcm_s32le -ac 6 " +
"-ar 48000 -f wav - | " +
"ffmpeg\\fdkaac --ignorelength -m 1 -o ouput_track.aac -"
};
Note that the actual command is a single string. (The quotes around the 0.0 look a bit strange, but that is what you have in your question.)
| is a shell pipe character, in java you'll have to either run this command in a shall (bash -c "the whole commandline | goes here"), or you'll have to run two processes (the one before the | and the one after), where the stdout of the first writes into the stdin of the second. For this, you'd typically use redirectOutput(Redirect.PIPE) and redirectInput(Redirect.PIPE).
I'm working on a Java macro that runs within another program as part of a computational fluid dynamics package. One thing that annoys me about this package is that the monitor going on standby seems to pause the simulations. But seeing as I have access to these macros I thought that I would add a section to change my power settings to keep the monitor awake.
I'm rather new to Java and so I found the easiest way of doing this would be to call PowerScript to do the actual settings changes. So far, I'm able to read the current state of the settings using the following (hidden for readability since this part works).
String command;
command = "powershell.exe $p = Get-CimInstance -Name root\\cimv2\\power -Class win32_PowerPlan -Filter \"IsActive=\'True\'\"; $p.ElementName";
Process powerShellProcess = Runtime.getRuntime().exec(command);
powerShellProcess.getOutputStream().close();
String line;
BufferedReader stdout = new BufferedReader(new InputStreamReader(
powerShellProcess.getInputStream()));
line = stdout.readLine();
System.out.println("The current power mode is: "+line);
stdout.close();
The next step would be to set the power settings using something like this:
String powerMode = "Balanced";
command = "powershell.exe $p = Get-CimInstance -Name root\\cimv2\\power -Class win32_PowerPlan -Filter \"ElementName=\'"+powerMode+"\'\"; Invoke-CimMethod -InputObject $p[0] -MethodName Activate";
System.out.println(command);
powerShellProcess = Runtime.getRuntime().exec(command);
powerShellProcess.getOutputStream().close();
new InputStreamReader(powerShellProcess.getInputStream());
The command prints properly as
powershell.exe $p = Get-CimInstance -Name root\cimv2\power -Class win32_PowerPlan -Filter "ElementName='Balanced'"; Invoke-CimMethod -InputObject $p[0] -MethodName Activate
When running that command (minus the "powershell.exe", of course) in PowerShell works perfectly, but when calling it from Java results in the -Filter "ElementName='Balanced'" returning null.
Can anyone tell me why the filter argument is not being passed properly? It works fine when filtering by "IsActive" as shown in the first part but not when filtering by "ElementName". Could it have something to do with the escape sequence nightmare around the element name?
Powershell is very finicky on its handling of quotes on the command line. The easy solution is to send in the query as
-Filter 'ElementName=\"Balanced\"'
For more info on this see
https://connect.microsoft.com/PowerShell/feedback/details/376207/executing-commands-which-require-quotes-and-variables-is-practically-impossible
I'm trying to execute unix commands thru a java program. Some of these commands involve an if-then-fi statement. Can this be done thru java / Runtime class? Seems like it only handles 1 command at a time.
I'm looking to do something like this:
grep 'Error One' SystemErr.log > $HOME/tempFiles/output.txt
grep 'Error Two' SystemErr.log >> $HOME/tempFiles/output.txt
grep 'Error Three' SystemErr.log >> $HOME/tempFiles/output.txt
.
.
if [ -s $HOME/tempFiles/output.txt ]
then
mail -s "Subject here" "a#b.com" < $HOME/tempFiles/output.txt
fi
Basically, I just want to email the file (results) if the grep found anything.
I want to use java instead of a direct shell script so that the errors I search for can be database-driven, easier to change.
I know I could read the file myself in java and search/parse it myself. But grep and other unix commands have a lot of built-in functionality I want to use to make it easier.
Any ideas, or am I totally on the wrong track?
Here is some code, using simpler commands, but basically equivalent:
public static void main( String[] args ) throws Exception {
try {
ProcessBuilder pb = new ProcessBuilder( "/bin/bash", "-c",
"echo one >/tmp/xxx && echo two >>/tmp/xxx && " +
"if [ -s /tmp/xxx ]; then cp /tmp/xxx /tmp/yyy; fi" );
File log = new File( "/tmp/log.txt" );
pb.redirectOutput(ProcessBuilder.Redirect.appendTo(log));
Process process = pb.start();
process.waitFor();
} catch( Exception e ){
// ...
} catch( Error e ){
// ...
}
}
The trick is to put it all into a single shell command so that you can call /bin/bash with the -c command option.
If composing this command is too complicated, write a shell file and source that.