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

Issue

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.

Solution

^{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 ''.

Answered By - Jonathan Leffler