0

This code check if the last 4 characters of the variable $1 correspond to the string in variable $2 anticipated by a dot.

    if [ "${1: -4}" == ".$2" ]; then
        return 0
    else
        return 1
    fi

// true with $1 = example.doc and $2 = doc
// false with $1 = example.docx and $2 = doc

how can I replace the hardcoded 4 with the following variable $CHECKER_EXTENSION calculated like this?

    LENGTH_EXTENSION=${#2}
    CHECKER_EXTENSION=$(( LENGTH_EXTENSION + 1 ))

Thanks in advance

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6
  • Please add your desired output (no description) for that sample input to your question (no comment). Commented Apr 29, 2020 at 19:44
  • 1
    If the part you wish to get is always behind a dot (.) you may use: ${url##*.} instead of counting the number of chars you need to remove Commented Apr 29, 2020 at 19:46
  • @0stone0: That's a good point; but note that it will give the wrong result if $2 contains a dot (if that's possible). Commented Apr 29, 2020 at 19:52
  • @Cyrus I needed to know how to replace the hardcoded 4 with a variable, the goal is to check if a filename and a given extension are the same, but that was not the question. I use the dot as an extra check in the filename. Commented Apr 29, 2020 at 20:07
  • Replace 4 with $variable. Commented Apr 29, 2020 at 21:43

4 Answers 4

Reset to default
3

You don't need to strip the leading characters from $1, since bash's [[ ]] can do wildard-style pattern matching:

if [[ "$1" = *".$2" ]]; then
    ...

Note that you must use [[ ]], and not [ ], to get pattern-matching rather than simple string equality testing. Also, having the * unquoted but .$2 in quotes means the * will be treated as a wildcard, but $2 will be matched literally even if it contains wildcardish characters. If you want $2 to also be treated as a pattern (e.g. you could use [Jj][Pp][Gg] to match "jpg" and "JPG" and combinations), leave off the quotes:

if [[ "$1" = *.$2 ]]; then

Oh, and the quotes around $1 don't matter in this particular situation; but I tend to double-quote variables unless there's a specific reason not to.

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1 Comment

+1. This is one of those cases where what the OP is asking for isn't really what the OP should use in his/her specific situation. :-)
2

The offset is interpreted as an arithmetic expression (the same syntax as inside $(( ... ))), so you can write:

    if [ "${1: -CHECKER_EXTENSION}" == ".$2" ]; then

You can even eliminate the CHECKER_EXTENSION variable and write:

    if [ "${1: -(${#2} + 1)}" == ".$2" ]; then
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1

You may use it like this:

myfunc() {
   local num_ext=$(( ${#2} + 1 ))

   [[ "${1: -$num_ext}" = ".$2" ]]
}
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0

If your execution environment meets the following criteria, you can choose a more concise method.

  • The requirement is to check if the extension is as expected
  • I'm using Bash
#!/usr/bin/env bash

if [[ ${1##*.} == "${2}" ]]; then
  echo "same"
else
  echo "not same"
fi

Execute test.

# test case 1
$ ./sample.sh test.txt txt
same

# test case 2
$ ./sample.sh test.exe txt
not same

# test case 3
$ ./sample.sh test.exe.txt txt
same

# test case 4
$ ./sample.sh test.txt.exe txt
not same

# test case 5
$ ./sample.sh test.txt.exe exe
same
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