Use regex to check if particular directory has folders starting with specific word

Question

I am writing a script that checks a certain directory for any sub-directories starting with a specific word.

Here is my script thus far:

#!/bin/bash

function checkDirectory() {
    themeDirectory="/usr/share/themes"
    iconDirectory="/usr/share/icons"
    # I don't know what to put for the regex. 
    regex=

    if [ -d "$themeDirectory/$regex" && -d "$iconDirectory/$regex" ]; then
       echo "Directories exist."
    else
       echo "Directories don't exist."
    fi
}

So, how would you use regex to check if a particular directory has any folders starting with a specific word?

Answer 1

-d doesn't accept regexes, it accepts filenames. If you just want to check a simple prefix, a wildcard is enough:

exists=0
shopt -s nullglob
for file in "$themeDirectory"/word* "$iconDirectory"/* ; do
    if [[ -d $file ]] ; then
        exists=1
        break
    fi
done
if ((exists)) ; then
    echo Directory exists.
else
    echo "Directories don't exist."
fi

nullglob makes the wildcards expand to empty lists if there are no matches. In a larger script, change its value in a subshell, or set back the old value once you don't need it.

Answer 2

If you only want to find directories matching a given pattern/prefix, I think you could just use find:

find /target/directory -type d -name "prefix*"

or, if you only want immediate subdirectories:

find /target/directory -maxdepth 1 -type d -name "prefix*"

Of course, there's also -regexif you need an actual regex match. (caveat: I can't remember if -maxdepth is a gnu-ism.)

(update) Right, you wanted an if statement. Find always returns a zero, so we can't use the return value to check if anything was found (unlike with grep). But we can e.g. count the lines. Pipe the output through wc to get the count, then see if it's not zero:

if [ $(find /target/directory -type d -name "prefix*" | wc -l ) != "0" ] ; then
    echo something was found
else
    echo nope, didn't find anything
fi

Answer 3

The name of your variable regex will not be well chosen but consider setting the value to "$1" like regex="$1". Next step is to change the if statement from:

if [ -d "$themeDirectory/$regex" && -d "$iconDirectory/$regex" ]; then

to

if [ -d "$themeDirectory/$regex" ] && [ -d "$iconDirectory/$regex" ]; then

The script will become:

function checkDirectory() {
    themeDirectory="/usr/share/themes"
    iconDirectory="/usr/share/icons"
    # I don't know what to put for the regex. 
    regex="$1"

    if [ -d "$themeDirectory/$regex" ] && [ -d "$iconDirectory/$regex" ]; then
       echo "Directories exist."
    else
       echo "Directories don't exist."
    fi
}

From a shell you can source your script by:

. /path/to/script

And the function is ready for use:

checkDirectory test
Directories don't exist.