More Working with CSV Files from the Command Line

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How to extract and manipulate CSV data using the command line.

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Process Substitution

mattcen's picture

I've never seen this 'Process Substitution' done before! I just had a quick look at it in the Bash man page. It's something that would've been very used to me in a few occasions over the past few months. Perhaps I haven't heard of it because it's not part of the Posix standard?

Very cool! Thanks for showing us.


Matthew Cengia

Useful even if not often used

Mitch Frazier's picture

Not something I use very often, it seems a bit "involved" so it doesn't always occur to me at first, but it is useful.

According to wikipedia ksh, zsh, and rc also support process substitution.

Mitch Frazier is an Associate Editor for Linux Journal.


Anonymous Blub's picture

these videos are great. i'd love to be able to follow up and learn for myself.

is there a chance you could post the session text so we could copy/paste/play?

thanks, AB

Good Idea

Mitch Frazier's picture

Here's a shell script that contains the code from this video and the previous one:


# Extract emails:
# Could also do: grep -i -o '[^,]*@[^,]*' stuff.csv
cut -f 3 -d , stuff.csv

# Use emails to extract lines:
for i in $(cut -f 3 -d , stuff.csv | sort --ignore-case | uniq --ignore-case)
        grep -i -F "$i" stuff.csv | head -n 1

# Make sure posix mode is OFF so process substitution works "<(...)" syntax.
set +o posix

# Use emails to de-dupe a file and then extract lines:
for i in $(comm -23 \
                <(cut -f 3 -d , stuff.csv | sort --ignore-case | uniq --ignore-case) \
                <(cut -f 3 -d , nostuff.csv | sort --ignore-case | uniq --ignore-case))
        grep -i -F "$i" stuff.csv | head -n 1

Here's stuff.csv:


And nostuff.csv:


Mitch Frazier is an Associate Editor for Linux Journal.

the comm command is great.

Anonymous's picture

the comm command is great. set difference on the command line has always been useful to me. thanks for the example!

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