Questions about shell scripts, executable files that are interpreted by a shell (bash, zsh, etc.). Check scripts with https://shellcheck.net before posting.
Shell scripting is often considered a simple domain-specific programming language. Typical operations performed by shell scripts include file manipulation, program execution, and printing text.
I notice that some scripts which I have acquired from others have the shebang #!/path/to/NAME while others (using the same tool, NAME) have the shebang #!/usr/bin/env NAME . Both seem to work properly. In tutorials (on Python, for example), there…
I have been looking at a few scripts other people wrote (specifically Red Hat), and a lot of their variables are assigned using the following notation VARIABLE1="${VARIABLE1:-some_val}" or some expand other variables VARIABLE2="${VARIABLE2:-`echo…
This question is a sequel of sorts to my earlier question . The users on this site kindly helped me determine how to write a bash for loop that iterates over string values. For example, suppose that a loop control variable fname iterates over the…
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 string into the script. How do I approach doing…
I know this question has probably been answered before. I have seen many threads about this in various places, but the answers are usually hard to extract for me. I am looking for help with an example usage of the 'sed' command. Say I wanted to act…
I would like to change a file extension from *.txt to *.text . I tried using the basename command, but I'm having trouble changing more than one file. Here's my code: files=`ls -1 *.txt` for x in $files do mv $x "`basename $files .txt`.text" done…
Noone should need 10 years for asking this question, like I did. If I were just starting out with Linux, I'd want to know: When to alias, when to script and when to write a function? Where aliases are concerned, I use aliases for very simple…
Take the following script: #!/bin/sh sed 's/(127\.0\.1\.1)\s/\1/' [some file] If I try to run this in sh ( dash here), it'll fail because of the parentheses, which need to be escaped. But I don't need to escape the backslashes themselves (between…
I would like to remove all leading and trailing spaces and tabs from each line in an output. Is there a simple tool like trim I could pipe my output into? Example file: test space at back test space at front TAB at end TAB at front sequence of some…
… or an introductory guide to robust filename handling and other string passing in shell scripts. I wrote a shell script which works well most of the time. But it chokes on some inputs (e.g. on some file names). I encountered a problem such as the…
I need to find my external IP address from a shell script. At the moment I use this function: myip () { lwp-request -o text checkip.dyndns.org | awk '{ print $NF }' } But it relies on perl-libwww , perl-html-format , and perl-html-tree being…
While running a script, I want to create a temporary file in /tmp directory. After execution of that script, that will be cleaned by that script. How to do that in shell script?
The following bash syntax verifies if param isn't empty: [[ ! -z $param ]] For example: param="" [[ ! -z $param ]] && echo "I am not zero" No output and its fine. But when param is empty except for one (or more) space characters, then the case is…
I'm reading an example bash shell script: #!/bin/bash # This script makes a backup of my home directory. cd /home # This creates the archive tar cf /var/tmp/home_franky.tar franky > /dev/null 2>&1 # First remove the old bzip2 file. Redirect errors…
