To replace the first occurrence of a pattern with a given string, use ${parameter/pattern/string}: #!/bin/bash firstString=”I love Suzi and Marry” secondString=”Sara” echo “${firstString/Suzi/”$secondString”}” # prints ‘I love Sara and Marry’ To replace all occurrences, use ${parameter//pattern/string}: message=”The secret code is 12345″ echo “${message//[0-9]/X}” # prints ‘The secret code is XXXXX’ (This is documented in the … Read more
If you really want to use single quotes in the outermost layer, remember that you can glue both kinds of quotation. Example: alias rxvt=”urxvt -fg “”‘”‘#111111′”‘”‘ -bg ‘”‘”‘#111111′”‘” # ^^^^^ ^^^^^ ^^^^^ ^^^^ # 12345 12345 12345 1234 Explanation of how ‘”‘”‘ is interpreted as just ‘: ‘ End first quotation which uses single quotes. … Read more
There are two typical ways of declaring a function. I prefer the second approach. function function_name { command… } or function_name () { command… } To call a function with arguments: function_name “$arg1” “$arg2” The function refers to passed arguments by their position (not by name), that is $1, $2, and so forth. $0 is … Read more
Revised Answer (Feb 12, 2014) the_world_is_flat=true # …do something interesting… if [ “$the_world_is_flat” = true ] ; then echo ‘Be careful not to fall off!’ fi Original Answer Caveats: https://stackoverflow.com/a/21210966/89391 the_world_is_flat=true # …do something interesting… if $the_world_is_flat ; then echo ‘Be careful not to fall off!’ fi From: Using boolean variables in Bash The reason … Read more
In bash (>=4.2) it is preferable to use printf’s built-in date formatter (part of bash) rather than the external date (usually GNU date). As such: # put current date as yyyy-mm-dd in $date # -1 -> explicit current date, bash >=4.3 defaults to current time if not provided # -2 -> start time for shell … Read more
You should use #!/usr/bin/env bash for portability: different *nixes put bash in different places, and using /usr/bin/env is a workaround to run the first bash found on the PATH. And sh is not bash.
You could do this, which facilitates reading: >&2 echo “error” >&2 copies file descriptor #2 to file descriptor #1. Therefore, after this redirection is performed, both file descriptors will refer to the same file: the one file descriptor #2 was originally referring to. For more information see the Bash Hackers Illustrated Redirection Tutorial.
The are various ways: POSIX standard tr $ echo “$a” | tr ‘[:upper:]’ ‘[:lower:]’ hi all AWK $ echo “$a” | awk ‘{print tolower($0)}’ hi all Non-POSIX You may run into portability issues with the following examples: Bash 4.0 $ echo “${a,,}” hi all sed $ echo “$a” | sed -e ‘s/\(.*\)/\L\1/’ hi all # … Read more
What is sh? sh (or the Shell Command Language) is a programming language described by the POSIX standard. It has many implementations (ksh88, Dash, …). Bash can also be considered an implementation of sh (see below). Because sh is a specification, not an implementation, /bin/sh is a symlink (or a hard link) to an actual … Read more
It is: if [ $# -eq 0 ] then echo “No arguments supplied” fi The $# variable will tell you the number of input arguments the script was passed. Or you can check if an argument is an empty string or not like: if [ -z “$1” ] then echo “No argument supplied” fi The … Read more