How to get the first column of every line from a CSV file?

Question

How do get the first column of every line in an input CSV file and output to a new file? I am thinking using awk but not sure how.

Rudelson

can the first column contain , ? – Negotiation

More general: what CSV dialect does your file use? – Calliecalligraphy

Answer 1

Try this:

 awk -F"," '{print $1}' data.txt

It will split each input line in the file data.txt into different fields based on , character (as specified with the -F) and print the first field (column) to stdout.

Meredith

@downvoter .. A downvote without explanation doesn't help anyone (OP, SO or me). This is a functional solution that meets OP's stated requirements. I am happy to correct errors or improve my answer but that requires constructive feedback. – Meredith

I didn't downvote, but I also won't upvote: It's the use of awk where cut would do. It smacks of one-size-fits-all-ism; using perl or sed would be just as bad. Not wrong, just not really right. Now, if you had answered with an awk script that handled a csv file like "last, first",field2,field3 correctly, that would have been more appropriate. – Frontogenesis

@Sorpigal ..and I wouldn't have downvoted you if you had used cut in place of awk :-) .. either tool is fine for this. FWIW, OP mentioned awk in their post, and I upvoted a "competing" cut solution (it could have been yours had you posted). It's not a religion, it's a small task that needed to be done, and I picked one of several tools to do it. – Meredith

@Meredith May be the down-voter saw your solution as an incomplete one. OP wanted the output to a new file. :P – Riding

@JaypalSingh Ha ha .. yes, perhaps, but that would be somewhat petty (anyone using a linux system most likely would know how to use io redirection) and could have easily been noted by the downvoter (and then trivially fixed). OP didn't seem troubled by that (nor do all of the answers provide this). Doesn't matter, it solved OP's problem which is main reason for the Q&A. – Meredith

@Levon: I was trying to suggest a motivation for a down vote, that's all. There was no need for me to post anything since the topic had already been covered sufficiently and completely before I saw it. – Frontogenesis

I am a total newbie to Shell scripting. Can anyone explain me how to write this when the separation is tab instead of comma? – Baneful

@Baneful I'm pressed for time right now, so can't test it, but try using \t in place of the comma above – Meredith

Answer 2

Can be done:

$ cut -d, -f1 data.txt

Calliecalligraphy

This is by far the fastest of all the answers, for a large CSV file. My situation involves a 2GB file containing rows that look like 2021-12-26,472406,616125. To get the first column, this answer using cut takes 5.1 seconds. Awk (awk -F, '{print $1}') takes 40 seconds. Perl (perl -F, -lane 'print $F[0]') takes 49 seconds. Ripgrep (rg -o '^[^,]+') takes 27 seconds. GNU grep (grep -o '^[^,]\+') takes 177 seconds. – Trickery

Answer 3

echo "a,b,c" | cut -d',' -f1 > newFile

Eisenhower

The 's around the delimiter are not necessary if the shell can handle it unescaped. – Calliecalligraphy

+1 to counter the down vote. This answer is arguably the most complete and correct! – Frontogenesis

Answer 4

Input

a,12,34
b,23,56

Code

awk -F "," '{print $1}' Input

Format

awk -F <delimiter> '{print $<column_number>}' Input

Segalman

Answer 5

This can be achieved using grep:

$ grep -o '^[^,]\+' file.csv

Sutphin

Answer 6

Using Perl:

perl -F, -lane 'print $F[0]' data.txt > data2.txt

These command-line options are used:

• -n loop around every line of the input file
• -l removes newlines before processing, and adds them back in afterwards
• -a autosplit mode – split input lines into the @F array. Defaults to splitting on whitespace.
• -e execute the perl code
• -F autosplit modifier, in this case splits on ,

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If you want to modify your original file in-place, use the -i option:

perl -i -lane 'print $F[0]' data.txt

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If you want to modify your original file in-place and make a backup copy:

perl -i.bak -lane 'print $F[0]' data.txt

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If your data is whitespace separated rather than comma-separated:

perl -lane 'print $F[0]' data.txt

Gaily