hshantanu hshantanu - 6 months ago 14
Linux Question

Cut and remove a string from another string in shell script

I have a following string in a shell script.

var="rule:access=allow,default=default value,OTHER=0,SOMETHING=1"


I need to remove "default=default value" from $var.
Thus, the final string will become as follows:

var="rule:access=allow,OTHER=0,SOMETHING=1"


NOTE: The value after default may be anything. It could be "default=something else". It is not fixed. I need to remove that text.
How can this be done?

Answer

Answer for revised question

$ echo "$var" | sed 's/default=[^,]*,//'
rule:access=allow,OTHER=0,SOMETHING=1

If we want to update the value of var, we use command substitution:

$ var="$(echo "$var" | sed 's/default=[^,]*,//')"
$ echo "$var"
rule:access=allow,OTHER=0,SOMETHING=1

Answer for original question

Using bash

To remove default=default value,, use pattern substitution:

$ var="${var/default=default value,/}"
$ echo "$var"
rule:access=allow,OTHER=0,SOMETHING=1

This feature is documented in man bash:

${parameter/pattern/string}
Pattern substitution. The pattern is expanded to produce a pattern just as in pathname expansion. Parameter is expanded and the longest match of pattern against its value is replaced with string. If pattern begins with /, all matches of pattern are replaced with string. Normally only the first match is replaced. If pattern begins with #, it must match at the beginning of the expanded value of parameter. If pattern begins with %, it must match at the end of the expanded value of parameter. If string is null, matches of pattern are deleted and the / following pattern may be omitted. If parameter is @ or *, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *, the substitution operation is applied to each member of the array in turn, and the expansion is the resultant list.

Using sed

$ var="$(echo "$var" | sed 's/default=default value,//')"
$ echo "$var" 
rule:access=allow,OTHER=0,SOMETHING=1