The bash script does many things. However, at beginning it should start if the input passed to the script is a directory path. For example, right way of telling directory path is "/var/lib/test", and incorrect way is "/var/%%^?/test".

where test is a directory and not a file.

The directory path can contain characters. [A-Za-z0-9/_-]

My script is as below -

if [[ ! ${dirPath} =~ "^/[A-Za-z0-9/_-]+$" ]]; then
    echo "Success"
    echo "Failure"

Here, dirPath can have any path provided from another script.

please let me know the error here.

  • I don't exactly understand the question. So the above script returns Success. Is that expected? Can you give some examples of when it should return Failure and Success? – Sparhawk Sep 28 '18 at 11:45
  • Is the issue the characters in the path? /var/%%^?/test is a valid pathname on Unix. Would it be enough to test whether the given path denotes an existing directory? – Kusalananda Sep 28 '18 at 11:45
  • The script should test if the given directory path is valid or not. Valid directory path includes characters - [A-Za-z0-9_-/] – user7290726 Sep 28 '18 at 11:50
  • 1
    @Goro Inside [...] in a regular expression, there are no delimiters. Even backslashes would be taken as literal backslashes. – Kusalananda Sep 28 '18 at 12:23
  • 1
    @Goro, Bash's =~ doesn't take slashes to delimit the regex – ilkkachu Sep 28 '18 at 12:24
if [[ ! ${dirPath} =~ "^/[A-Za-z0-9/_-]+$" ]]; then
    echo "Success"

This will test $dirPath against the literal string ^/[A-Za-z0-9/_-]+$, and invert the result. In other words, it will print Success when $dirPath is anything other than that literal string. This is because quoted characters in a regex lose their special meaning in current versions of Bash, and of course the ! works to invert the test.

If you want to test that variable against the actual regex, it's easiest to put the regex in a variable first, and leave it unquoted (using a variable may not be strictly necessary, but avoids some parsing issues with complex regexes):

if [[ ${dirPath} =~ $re ]]; then
    echo "'$dirPath' starts with a slash, and is composed of alphanumerics, hyphens, underscores and slashes only"
    echo "'$dirPath' is of a forbidden format"

Of course, if you want to test if that path is an existing directory, then you'd use -d:

if [[ -d $dirPath ]]; then
    echo "'$dirPath' exists and is a directory

Remove the quotes from the regex:

[[ ! "${dirPath}" =~ ^/[A-Za-z0-9/_-]+$ ]]

Quoting the regex forces string matching since Bash 3.2.

Compare this question on Stackoverflow.

Note: while this fixes your script, it does not properly check if the path is a correct directory path. Refer to @Kusalanandas answer how to do a proper check.

  • Someone out there is right now waiting for new Q or A to immediate downvote. – pLumo Sep 28 '18 at 11:59
  • 2
    what's going on? 3 downvotes to a valid answer that provides information from an answer from SO that has 102 upvotes. Still nothing in the comments. – pLumo Sep 28 '18 at 12:02
  • Also, four upvotes... – Kusalananda Sep 28 '18 at 13:40

This answer focuses on the first part of the question which (currently) reads:

However, at beginning it should start if the input passed to the script is a directory path.

The rest of the question is an attempt at doing this by matching a particular regular expression against a pathname to try to figure out whether it's a valid directory pathname.

A script should not generally impose an arbitrary naming scheme on the user's directories or files without reason. The pathname /var/%%^?/test is perfectly valid on a system where there exists a directory called %%^? under /var and where this directory contains a subdirectory called test.

What your script is really concerned about is whether it's given a pathname to an existing directory. Whatever the directory path is is less important.

This may be done with



if [ ! -d "$dirPath" ]; then
    printf '"%s" is not a valid directory path\n' "$dirPath" >&2
    exit 1

After this if-statement, you know that "$dirPath" is the path to an existing directory. The pathname to the directory is (in the above code) taken from the first command line argument.

  • 1
    @RoVo Your initial comment makes some sense though, so I will clarify. Thanks! – Kusalananda Sep 28 '18 at 12:24
  • thanks :) you answered the question correctly but the title of the Q is very misleading. – pLumo Sep 28 '18 at 13:15

to check if its file or dir you don't need regex - use:

if [ -d "${testpath}" ] ; then
    echo "$testpath is a directory";

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