SED command not being run from bash script

Question

I have written a bash script which calls a sed command (amongst other things) on a file to complete a find/replace of 2 different strings.

The trouble is, after running the script, I check the files and nothing has been updated. However, if I run the commands that are being produced (I echo them as output anyway) then they work.

For example, inside the script I have:

echo "/usr/local/bin/sed -i -e 's/${String1}/${String1R}/g;s/\/${String2}\//\/${String2R}\//g' ${ROOT_DIR}/data/file.sql"
/usr/local/bin/sed -i -e 's/${String1}/${String1R}/g;s/\/${String2}\//\/${TString2R}\//g' ${ROOT_DIR}/data/file.sql

Running the script does not change file.sql; however, if I run the command that is printed to console e.g. /usr/local/bin/sed -i -e 's/file_name1/file_name2/g;s//path_substring1///path_substring2//g' /path/to/file/file.sql it works perfectly!

You use the word "string" a lot, but your script isn't doing string comparison, it's doing regexp comparison, is that OK? It will come back to bite you if "String1". for example, contains RE meta-characters such as ., ?, *, etc. — Ed Morton
– Ed Morton, Commented Nov 22, 2013 at 13:25

devnull · Accepted Answer · 2013-11-22 10:51:52Z

6

Use double quotes instead of single quotes. Single quotes would prevent variable expansion.

/usr/local/bin/sed -i -e "s/${String1}/${String1R}/g;s/\/${String2}\//\/${TString2R}\//g" ${ROOT_DIR}/data/file.sql

Moreover, it seems that your variables are path strings which might contain forward slashes, i.e. /. In that event use a different separator:

"s|${String1}|${String1R}|g"

Using a different separator would obviate the need of escaping / in the pattern and replacement.

answered Nov 22, 2013 at 10:51

devnull

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4 Comments

user2294382 Over a year ago

Thanks devnull. One thing, substituting / with | didn't work. Luckily, the path substrings should not contain any slashes however, it would be cleaner without having to escape them. Do you need to provide the separator as a separate argument?

devnull Over a year ago

@user2294382 I'm not sure why it didn't work for you. As an example, try executing the command: echo a/b/c | sed "s|/b/|//d//|g" and observe what it does.

user2294382 Over a year ago

Hmm strange that worked - i get a//d//c. I must have done something wrong. Thanks

devnull Over a year ago

@user2294382 Yes, that is precisely what was the expected output. I was attempting to illustrate the fact that you didn't need to escape the / in the pattern and the replacement. The pattern /b/ was replaced by //d// without escaping the slash.

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