The following command executes fine in bash:
Command:
bash -c "$(echo 'H4sIAArQ/mAAA1WMuw7CIBRAd77ihLJqtKuTg19hHIjetiQU0svl/1sn43weaeKJD4PnlI2R1w1bpOBA3kvF340ssX1Z1LmvUqyhsvWk8jl7nOQmP/2x9ZixSlXWqnLcYvlrw4VwJYxHOiW3AwCHgS2AAAAA' | base64 --decode | zcat)" - -a -b
Output:
Equal to or more than 2 arguments - -a -b
Wanted to know - how can I achieve this using Java's ProcessBuilder?
I tried the following:
ProcessBuilder processBuilder = new ProcessBuilder(args);
where args are:
bash
-c
"$(echo 'H4sIAArQ/mAAA1WMuw7CIBRAd77ihLJqtKuTg19hHIjetiQU0svl/1sn43weaeKJD4PnlI2R1w1bpOBA3kvF340ssX1Z1LmvUqyhsvWk8jl7nOQmP/2x9ZixSlXWqnLcYvlrw4VwJYxHOiW3AwCHgS2AAAAA' | base64 --decode | zcat)"
-
-a
-b
But I keep on getting the following error:
-: if: command not found
Process finished with exit code 127
Can someone please point out the issue here?
Command substitution results, in bash, don't go through all parsing steps. That means that compound commands like if aren't honored, command separators like ; have no syntactic meaning, etc.
If you want to override that and force an additional parsing pass, you need to use eval. Thus:
args = String[]{
"bash",
"-c",
"eval \"$(echo 'H4sIAArQ/mAAA1WMuw7CIBRAd77ihLJqtKuTg19hHIjetiQU0svl/1sn43weaeKJD4PnlI2R1w1bpOBA3kvF340ssX1Z1LmvUqyhsvWk8jl7nOQmP/2x9ZixSlXWqnLcYvlrw4VwJYxHOiW3AwCHgS2AAAAA' | base64 --decode | zcat)\"",
"-",
"-a",
"-b",
}
Why did this work when you ran it in a shell, instead of from a ProcessBuilder? Because that shell you ran it in would perform the command substitution in "$(...)", and put the results of that substitution in the text it passed to the child shell; so the substitution was already done at parsing time.
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 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.
I have gpg command which encrypts the file
gpg --batch --yes -o abc.csv.gpg -r 'balu shanmukh' -e A2.java
in the above command
--batch
--yes
-o
-r and -e are options
and balu shanmukh is the value.
the command is prepared dynamically and the command prepaed is the above. this command is being exected in commandline but when this command is running from
Runtime.getRuntime().exec(command);
am getting error message
as usage: gpg [options] [filename]
their is no problem with gpg classs path or anything because if i remove the single quote for the value which doesnt have space in between the command is getting executed properly from java.
only the problem when we have space in value . then its mandatory to use quote for value and if i use it . commad is not getting executed properly
I didnt understand the behaviour?
can any one help me to understand this behaviour
Don't use Runtime().exec(), and don't create the command as a single string. Instead, build a ProcessBuilder for your Process, and pass each switch to your command as an argument.
Here's a simple example:
Process process = new ProcessBuilder("gpg", "--foo", "-r", "some_file_name").start();
int exitStatus = process.waitFor();
PS: As others noted, do revisit your questions, and check the answers you think answer your question. People give some effort answering. If you think they helped, vote them up, or check their answer as the one that answered your question.
Good luck and welcome here ;)
Here's a simple example:
Process process = new ProcessBuilder("gpg", "--foo", "-r", "some_file_name").start();
int exitStatus = process.waitFor();
Sorry but that doesnt explain how you pass a single quoted string as an argument.
ie. to pass 'baku' as an argument.
"'baku'" does not work....
I'm trying to run this command to use ghostscript (from java) but Whether with single quote ' or " or nothing at all I get an error
Error: /undefinedfilename in ('c:\\Documents)
gswin32c.exe -q -dNOPAUSE -sDEVICE=tiffgray -sOutputFile=C:\polter.tiff -r300 'c:\Documents and Settings\polter.pdf' -c quit
any ideas?
use the short names for folders. short names are aliases which are using the 8.3 format. you can find the short name of a folder by using the dir /x command on the command prompt. your path will then look something like this: c:\docume~1\polter.pdf
Break up the arguments yourself:
String[] cmd = {
"gswin32c.exe",
"-q", "-dNOPAUSE", "-sDEVICE=tiffgray",
"-sOutputFile=C:\polter.tiff", "-r300",
"c:\Documents and Settings\polter.pdf",
"-c", "quit"
};
Runtime.getRuntime().exec(cmd);