Conditional statement using rexep with bash
bash, regex
Solution
Starting Note: Answer created with input from comments in question, especially in response of the last comment.
First, what is `[[`? It is a shell keyword.
samveen@maverick:~$ type [[
[[ is a shell keyword
This means that `[[` is an internal keyword of bash, not a command and thus will not work with other shells. Thus, your error output
scripts/ssidchecker.sh: 22: [[: not found
means that the shell you're using is probably
- Not bash
- A version of bash older than 2.02 (`[[` introduced in Bash-2.02)
Given that 2.02 is a really really old version (pre Y2K), all this just points to the fact that the shell you're using to run the script is probably not `/bin/bash`, instead probably being `/bin/sh` which is the most common path used for Bourne shell scripts `shebang` (the `#!`) line.
Please change that to `/bin/bash` or explicitly run `bash scripts/ssidchecker.sh` and you're good to go.
As to why the `else` section was always executed, the `[[` command not being found is the same as a failure (non-zero return value), from the viewpoint of `if`. Thus the `else` section is executed.
samveen@maverick:~$ /bin/whosyourdaddy
-bash: /bin/whosyourdaddy: No such file or directory
samveen@maverick:~$ echo $?
127
As a side note on portability, the bash hackers wiki also says the following about the `[[` keyword:
Amongst the major "POSIX-shell superset languages" (for lack of a better term) which do have `[[`, the test expression compound command is one of the very most portable non-POSIX features. Aside from the =~ operator, almost every major feature is consistent between Ksh88, Ksh93, mksh, Zsh, and Bash. Ksh93 also adds a large number of unique pattern matching features not supported by other shells including support for several different regex dialects, which are invoked using a different syntax from Bash's `=~`, though `=~` is still supported by ksh and defaults to ERE.
Thus your script will probably fail on the `=~` even if the shell supports `[[`, in case the shell isn't `bash` but supports `[[`.
Problem
I want to use the "conditional regexp" structure from bash, present since the third version of bash (circa 2004). It's supposed to go like this: ``` if [[ $string =~ $regexp ]]; then #do smthg else #do somthg else fi ``` So here's my code, following this structure, and its role is to check if the name contained in SSID is presend in the output from iw dev wlan0 link : ``` if [[ $(iw dev wlan0 link) =~ $SSID+ ]]; then #do sthming else echo "wrong network" fi ``` For some reason that i can't decipher, this statement works pretty well if I run it right into the bash shell, like ``` if [[ $(iw dev wlan0 link) =~ $SSID+ ]]; then echo found; else echo not found; fi ``` But if i run it inside the script its contained, it'll spit out: ``` scripts/ssidchecker.sh: 22: [[: not found ``` 22 being the line of the "fi" keyword. The strangest thing is that it will always execute the code contained in the "else" statement Is "not found" meant to indicate me that the regexp dind't find anything in that string? Is it a real error message?