Check for substring in Shell without Bashisms
dash-shell, linux, regex, shell
Solution
You can use `grep` with word boundary:
grep -E '-32\b' FILE
`\b` matches at a 'word boundary' = the location between an alphanumeric character and a non-alphanumeric character.
In the default locale, an 'alphanumeric character' (as the term is used above) means any character that is matched by the character class `[a-zA-Z0-9_]` (i.e. any number, any of the letters A–Z and underscore).
In an analogous way `\B` matches wherever there is not a word boundary (i.e. any location where the characters on either side of it are of the same type, either both alphanumeric characters, or both non-alphanumeric).
So if you wanted to make sure that the minus sign must be preceded by a non-alphanumeric character (e.g. space), as well, you would write the following:
grep -E '\B-32\b' FILE
This will match `xx -32 xx` (with a space before the minus) but not `xx-32 xx` (without the space). Since space and minus are both non-alphanumeric `\B` will match between them, but `\b` will not.
If you wanted to make sure that the minus sign is preceded by a alphanumeric character instead, you would write the following:
grep -E '\b-32\b' FILE
Which matches e.g. `x-32 x` (without the space), but not `x -32 x` (with a space before the minus).
Problem
I'm trying to write a shell script, and in it I have to look for the presence of -32 in a string. Unfortunately I have to do it without using any bashisms as it has to run on computers running Dash. I tried `case ${1+"$@"} in *-32*);;` but that will pick up something like -321. Is there a way to use a regex or something to look for just that flag? It can have other flags around it separated by spaces in the string. I think the regex I would need looks for -32 with either a space or end of line after. `-32(\s|$)` I'm pretty new to regexes so I'm not sure if that is the best way to do it. Any help would be appreciated! Thanks!