Questions about shell scripts, executable files that are interpreted by a shell (bash, zsh, etc.).

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11
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7answers
29k views

Calling multiple bash scripts and running them in parallel, not in sequence

Suppose that I have three (or more) bash scripts: script1.sh, script2.sh, and script3.sh. I would like to call all three of these scripts and run them in parallel. One way to do this is to just ...
11
votes
2answers
17k views

Bash scripting - loop until return value is 0

I need to umount something in my script, but sometimes it unmount's before all of the data has finished being copied and causes the umount to fail. I looked for a way to do a "blocking" umount, but I ...
11
votes
7answers
4k views

Shortest way to extract last 3 characters of base (minus suffix) filename

I'm trying to set a variable in an sh script to the last 3 characters of the base name of a file (by base name I mean without the path and without the suffix). I've succeeded in doing this but, purely ...
11
votes
3answers
10k views

Get path of current script when executed through a symlink

I have a utility consisting of a couple directories with some bash scripts and supporting files that will be deployed to several machines possibly in a different directory on each machine. The ...
11
votes
4answers
707 views

Fast method of splitting string from textfile?

I have a two text files: string.txt and lengths.txt String.txt: abcdefghijklmnopqrstuvwxyz lengths.txt 5 4 10 7 I want to get the file >Entry_1 abcde >Entry_2 fghi >Entry_3 jklmnopqrs ...
11
votes
2answers
4k views

Piping data to a process's stdin without causing EOF afterward

I have an executable that starts a user-interactive shell. I would like to, upon launch of the shell, inject a few commands first, then allow the user to have their interactive session. I can do this ...
11
votes
4answers
8k views

exit shell script from a subshell

Consider this snippet: stop () { echo "${1}" 1>&2 exit 1 } func () { if false; then echo "foo" else stop "something went wrong" fi } Normally when func ...
11
votes
4answers
6k views

How can I receive top-like CPU statistics from the shell?

I'm trying to get an accurate read of my used CPU (in percent) from top. This is the command I'm running for testing: top -n1 | awk '/Cpu\(s\):/ {print $2}' This returns: 10.7%us, Which is the ...
11
votes
1answer
1k views

How to generate a lot of (blank) images files?

For a test, I need to quickly create 1700 jpg-images (even blank) in a defined size 1000x706. I wonder if we could do this with a shell script or a program (like ImageMagick). I wish they called ...
11
votes
3answers
7k views

Add thousands separator in a number

In python re.sub(r"(?<=.)(?=(?:...)+$)", ",", stroke ) To split a number by triplets, e.g.: echo 123456789 | python -c 'import sys;import re; print re.sub(r"(?<=.)(?=(?:...)+$)", ",", ...
11
votes
1answer
523 views

Is there any way to tell if a shell script was killed with signal 9

I have a bash script (called from a java program) that keeps getting killed. I always catch the signal 15 with trap but then some other signal comes along that I suspect is signal 9 but am in ...
11
votes
5answers
7k views

Exit Google Chrome from terminal

Is there a way to cause google-chrome to quit, from the terminal, besides using killall google-chrome? I would like to be able to close it from a script without killing it.
11
votes
3answers
3k views

What does `1>>` and `2>>` mean in a bash script?

I have the following bash script, from what I understand >> is used to append the output of a command to an existing file instead of overwrite, but what is it doing in this case? This script is ...
11
votes
2answers
12k views

Regular expression in bash script

This is my first time bash scripting so I'm probably making an easy mistake. Basically, I'm trying to write a script that gets the groups of a user, and if they are in a certain group, it will log ...
11
votes
2answers
4k views

Using sed to color the output from a command on solaris

I have a ksh script that must work on both linux and solaris. I'm trying to color the output of specific commands. It works on linux (specifically RHEL6), but not on solaris (SunOS 5.10). Command ...
11
votes
5answers
17k views

Print Matching line and nth line from the matched line

I am trying to print the matched line and the 4th line from the matched line (line containing the expression I am searching for). I have been using the following code: sed -n 's/^[ \t]*//; /img ...
11
votes
2answers
369 views

How to start tailing a file that has not been yet created

I use tail to monitor the progress of jobs that I know will write their progress to disk. Almost always, I know which file they will create before they start running (the jobs are dispatched by a ...
11
votes
3answers
1k views

Are free shell accounts safe?

I am trying to identify how safe the free shell accounts provided by the likes of shellmix.com are. I have never used one myself but want to suggest it to someone interested in learning shell ...
11
votes
4answers
14k views

find -exec in bash script with variable expansion

I'm trying to run a command similar to the one below in a bash script. It should search through all subfolders of $sourcedir and copy all files of a certain type to the root level of $targetdir. ...
11
votes
4answers
354 views

Get the display width of a string of characters

What would be the closest to a portable way to get the display width (on a terminal at least (one that displays characters in the current locale with the correct width)) of a string of characters from ...
11
votes
3answers
26k views

How to set global environment variables at boot through a script, and have them available for an application that runs before login?

I have a service that runs at boot, and in that service it calls a bash script in the background that exports some environment variables. The problem I'm having is that those environment variables ...
11
votes
1answer
2k views

How do I make a shell script that sends output to a process

I'm currently running a server console program in a screen because I need to both read it and occasionally send commands. I'd like to run the app as a deamon in the background (start/stop it with ...
11
votes
3answers
1k views

Why does set -e not work inside () ||

I've run across some scripting like this recently: ( set -e ; do-stuff; do-more-stuff; ) || echo failed This looks fine to me, but it does not work! The set -e does not apply, when you add the ||. ...
10
votes
6answers
1k views

Is it possible to substitute “then” with brackets?

I first learned how to code in a C language, and using if ( code ) then code fi makes it really hard for me to read my code (don't ask why). Is there a substitute for then? Something like this: ...
10
votes
3answers
106k views

How to get IP Address using shell script? [duplicate]

Want to get the IP address using Shell script. Without knowing the eth0 or eth1 or eth2 How to get the particular IP address. I am not interest to get localhost address, want to get private IP ...
10
votes
6answers
716 views

Remove lines from a file depending on lines found in another file

File file1.txt contains lines like: /api/purchase/<hash>/index.html For example: /api/purchase/12ab09f46/index.html File file2.csv contains lines like: <hash>,timestamp,ip_address ...
10
votes
3answers
13k views

Prompt user to login as root when running a shell script

The problem I am getting is, when I enter the command, su - root at the beginning of my shell script file, it prompts the user to enter the password and then does NOT continue with the rest of the ...
10
votes
3answers
42k views

What does $# mean in shell?

What does $# mean in shell? I have code such as if [ $# -eq 0 ] then I want to understand what $# means, but Google search is very bad for searching these kinds of things.
10
votes
4answers
52k views

Storing output of command in shell variable [duplicate]

I have an operation using cut that I would like to assign result to a variable var4=echo ztemp.xml |cut -f1 -d '.' I get the error: ztemp.xml is not a command The value of var4 never gets ...
10
votes
8answers
5k views

cron Vs. sleep - which is the better one in terms of efficient cpu/memory utilization?

The Case: I need to run some commands/script at certain intervals of time and for this I have two options: set up a cron-job implement a loop with sleep in the script itself. Question: Which is ...
10
votes
4answers
52k views

How can I pass a command line argument into a shell script?

I know that shell scripts just run commands as if they were executed in at the command prompt. I'd like to be able to run shell scripts as if they were functions... That is, taking an input value or ...
10
votes
4answers
2k views

How can measure how long it takes my script to run AND include that in an email it generates?

I have a simple bash script that runs a series of checks (ping, nslookup, etc) and then sends an email report with the output of that data. I'd like the email to include information on how long it ...
10
votes
5answers
13k views

cd into all directories, execute command on files in that directory, and return to previous current directory

I'm attempting to write a script that will be run in a given directory with many single level sub directories. The script will cd into each of the sub directories, execute a command on the files in ...
10
votes
4answers
9k views

How to run parallel processes and combine outputs when both finished

I have a bash shell script in which I pipe some data through about 5 or 6 different programs then the final results into a tab delimited file. I then do the same again for a separate similar dataset ...
10
votes
1answer
1k views

How do you omit “./” when running scripts on current directory

On some tutorials over the internet they can run a script on the current directory without doing: ./script How do you omit this? I am using CentOS 5.6 x64. I want to run it this way script
10
votes
2answers
736 views

Is there a POSIX way of setting zeroth argument of a target application?

In bash you can use exec -a and in zsh you can alternatively also set ARGV0 to execute a program with a certain zeroth argument but is there also a POSIX way of doing so? As suggested in this one ...
10
votes
6answers
3k views

How to extract a key value pair from ps command

I am trying to extract application name from ps command: ps -af -u sas |grep "java"| grep -v "grep" above command produces the following: sas 24431 1 0 Oct10 ? 00:51:08 ...
10
votes
3answers
48k views

How can I concatenate a shell variable to other other parameters in my command lines?

How can I concatenate a shell variable to other other parameters in my command lines ? For example, #!/bin/sh WEBSITE="danydiop" /usr/bin/mysqldump --opt -u root --ppassword $WEBSITE > ...
10
votes
4answers
14k views

Bash script to detect the version control system by testing command return status

I am working on a bash script that I would like to work for several types of VCS. I am thinking of testing if a directory is a repo for a system by running a typical info command and checking the ...
10
votes
2answers
654 views

Having a problem with a shell script counting characters

I'm trying to learn the basics and I have run into an issue with my script counting the characters of a user's input. Here is my script, can someone point out where I'm going wrong please? ...
10
votes
6answers
13k views

Shell script for moving oldest files?

How do I write a script for moving just the 20 oldest files from one folder to another? Is there a way to grab the oldest files in a folder?
10
votes
3answers
48k views

Concatenating two variables with an underscore

I need to concatenate two variables to create a filename that has an underscore. Lets call my variables $FILENAME and $EXTENSION where filename is read from a file. FILENAME=Hello EXTENSION=WORLD.txt ...
10
votes
1answer
10k views

Trap, ERR, and echoing the error line

I'm trying to create some error reporting using a Trap to call a function on all errors: Trap "_func" ERR Is it possible to get what line the ERR signal was sent from? The shell is bash. If I do ...
10
votes
3answers
8k views

Loop through the lines of two files in parallel [closed]

The object of the script I'm making is to compare two series of files. The file names are themselves stored into two separate files, one path per line. My idea is to have two while read loops, one for ...
10
votes
2answers
3k views

Piping for loop output prevents local variable modification

I'm trying to write a simple bash function that takes, as its arguments, a number of files and/or directories. It should: Fully qualify the filenames. Sort them. Remove duplicates. Print all that ...
10
votes
3answers
936 views

What's a smart way to count the number of days since X?

I started working at my current position since November 17th 2014. I would like to know how many days have run up to now. Any ideas on how to use Linux to come up with a simple and nice solution ?
10
votes
2answers
3k views

nvm command not available in bash script

I am trying to build a script in in which nvm and eventually node will get installed. I have installed nvm with cURL. I see the modifications in the .profile or .bashrc file (both work) and when ...
10
votes
3answers
766 views

How can I use a variable as a case condition?

I am trying to use a variable consisting of different strings separated with a | as a case statement test. For example: string="\"foo\"|\"bar\"" read choice case $choice in $string) echo ...
10
votes
2answers
46k views

Cron job to delete files older than 3 days

I need to remove files older than 3 days with a cron job in 3 different directories. (these 3 directories are children of a parent directory /a/b/c/1 & /a/b/c/2 & /a/b/c/3) Can this be done ...
10
votes
3answers
8k views

Diff, show modified line from right file only

I have file a and b and I would like to output lines of b that changed since it was cloned from a. Just the modified lines, no surrounding context, no diff offset marks. How can I do that using shell ...