CODEWITHSUNDEEP
bashshell
Amit
Amit

Reputation: 101

Remove first two characters from a column in a text file excluding the headers

I want to remove the first two characters of a column in a text file. I am using the below but this is also truncating the headers.

sed -i 's/^..//' file1.txt

Below is my file:

FileName,Age
./Acct_Bal_Tgt.txt,7229
./IDQ_HB1.txt,5367
./IDQ_HB_LOGC.txt,5367
./IDQ_HB.txt,5367
./IGC_IDQ.txt,5448
./JobSchedule.txt,3851

I want the ./ to be removed from each line in the file name.

Upvotes: 1

Views: 547

Answers (2)

Jonathan Leffler
Jonathan Leffler

Reputation: 754400

Transferring comments to an answer, as requested.

Modify your script to:

sed -e '2,$s/^..//' file1.txt

The 2,$ prefix limits the change to lines 2 to the end of the file, leaving line 1 unchanged.

An alternative is to remove . and / as the first two characters on a line:

sed -e 's%^[.]/%%' file1.txt

I tend to use -e to specify that the script option follows; it isn't necessary unless you split the script over several arguments (so it isn't necessary here where there's just one argument for the script). You could use \. instead of [.]; I'm allergic to backslashes (as you would be if you ever spent time working out whether you needed 8 or 16 consecutive backslashes to get the right result in a troff document).

Advice: Don't use the -i option until you've got your script working correctly. It overwrites your file with the incorrect output just as happily as it will with the correct output. Consequently, if you're asking about how to write a sed script on SO, it isn't safe to be using the -i option. Also note that the -i option is non-standard and behaves differently with different versions of sed (when it is supported at all). Specifically, on macOS, the BSD sed requires a suffix specified; if you don't want a backup, you have to use two arguments: -i ''.

Upvotes: 1

Timur Shtatland
Timur Shtatland

Reputation: 12367

Use this Perl one-liner:

perl -pe 's{^[.]/}{}' file1.txt > output.txt

The Perl one-liner uses these command line flags:
-e : Tells Perl to look for code in-line, instead of in a file.
-p : Loop over the input one line at a time, assigning it to $_ by default. Add print $_ after each loop iteration.

s{^[.]/}{} : Replace a literal dot ([.]) followed by a slash ('/'), found at the beginning of the line (^), with nothing (delete them). This does not modify the header since it does not match the regex.

If you prefer to modify the file in-place, you can use this:

perl -i.bak -pe 's{^[.]/}{}' file1.txt

This creates the backup file file1.txt.bak.

SEE ALSO:
perldoc perlrun: how to execute the Perl interpreter: command line switches
perldoc perlrequick: Perl regular expressions quick start

Upvotes: 0

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