How to replace .. from string in bash script?

Question

I have to remove .. character from a file in Bash script. Example:

I have some string like:

some/../path/to/file
some/ab/path/to/file

And after replace, it should look like

some/path/to/file
some/ab/path/to/file

I have used below code

DUMMY_STRING=/../
TEMP_FILE=./temp.txt
sed s%${DUMMY_STRING}%/%g ${SRC_FILE} > ${TEMP_FILE}
cp ${TEMP_FILE} ${SRC_FILE}

It is replacing the /../ in line 1; but it is also removing the line /ab/ from second line. This is not desired. I understand it is considering /../ as some regex and /ab/ matches this regex. But I want only those /../ to be replaced.

Please provide some help.

Thanks,

NN

Jonathan Leffler · Accepted Answer · 2012-09-13 07:25:36Z

3

The . is a metacharacter in sed meaning 'any character'. To suppress its special meaning, escape it with a backslash:

sed -e 's%/\.\./%/%g' $src_file > $temp_file

Note that you are referring to different files after you eliminate the /../ like that. To refer to the same name as before (in the absence of symlinks, which complicate things), you would need to remove the directory component before the /../. Thus:

some/../path/to/file
path/to/file

refer to the same file, assuming some is a directory and not a symlink somewhere else, but in general, some/path/to/file is a different file (though symlinks could be used to confound that assertion).

$ x="some/../path/to/file
> some/ab/path/to/file
> /some/path/../to/another/../file"
$ echo "$x"
some/../path/to/file
some/ab/path/to/file
/some/path/../to/another/../file
$ echo "$x" | sed -e 's%/\.\./%/%g'
some/path/to/file
some/ab/path/to/file
/some/path/to/another/file
$ echo "$x" | sed -e "s%/\.\./%/%g"
some/path/to/file
some/ab/path/to/file
/some/path/to/another/file
$ echo "$x" | sed -e s%/\.\./%/%g
some/path/file
some/path/file
/some/path/to/another/file
$ echo "$x" | sed -e s%/\\.\\./%/%g
some/path/to/file
some/ab/path/to/file
/some/path/to/another/file
$

Note the careful use of double quotes around the variable "$x" in the echo commands. I could have used either single or double quotes in the assignment and would have gotten the same result.

Test on Mac OS X 10.7.4 with the standard sed (and shell is /bin/sh, aka bash 3.2.x), but the results would be the same on any system.

edited Sep 13, 2012 at 7:25

answered Sep 13, 2012 at 6:24

Jonathan Leffler

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3 Comments

Niranjan Over a year ago

This is not working as desired. It is also removing "/tx/" which I do not want. I want only that sequence "/../" should be replaced by "/".

Jonathan Leffler Over a year ago

@Niranjan: Are you using single quotes or double quotes around the sed script? They are not interchangeable — at least, not in this context. Or are you still not using any quotes? If you do not use single quotes, you have to use more backslashes. As a rule of thumb, enclose sed scripts in single quotes unless you need to interpolate a shell variable.

Niranjan Over a year ago

Got the point Jonathan. I was not using any quote in SED command at all. Your suggestion was proposing to use single quote. That single quote sed -e 's%/\.\./%/%g' ${SRC_FILE} > ${TEMP_FILE} solved the problem. Appreciate your help. Thank you very much.

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