Objective: Escape or append a ‘\’ to reserved characters (e.g &, \, |, ?, *, etc) found on a string variable in bash.
Before we look at the solution, let’s take a closer look at the problem. Suppose, we have a shell variable assigned as shown below.
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$ evar='VAR_&_\_|_?_*_ESCAPE' |
Now, let’s try to use the variable in sed for search and replace. Let’s replace the occurrence of ‘__VAR__‘ to the contents of the variable $evar.
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$ echo __VAR__ | sed -e "s/__VAR__/$evar/" VAR___VAR____|_?_*_ESCAPE |
As you can see, the output is wrong. The output should be the contents of the variable $evar. We will need to escape the string found in the variable $evar before we pass it to sed.
The solution to insert escape sequences to the string variable is to use the shell builtin printf function with the “%q” format specifier as shown in the syntax below.
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$ printf "%q" "$evar" VAR_\&_\\_\|_\?_\*_ESCAPE |
To use it within sed, use the following syntax.
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$ echo __VAR__ | sed -e "s/__VAR__/$(printf "%q" "$evar")/" VAR_&_\_|_?_*_ESCAPE |
This time, the output is the same as the contents of the variable.
Mohamed Ibrahim
ibrahim = { interested_in(unix, linux, android, open_source, reverse_engineering); coding(c, shell, php, python, java, javascript, nodejs, react); plays_on(xbox, ps4); linux_desktop_user(true); }
