Shell Scripting

Hi there!

Usually, sed can be used in different ways, but most of the time we use it to match lines in a file against a fixed regexp. Some examples:

This replaces ocurrences of regexp for "foo":

sed 's/regexp/foo/g' < myfile

This prints all lines that have "foo", but will change the first "o" in the line for an "a":

sed -n '/foo/s/o/a/p' < myfile

and so on...

But I tried to do a different thing, with no success: can I pass to sed a file with a bunch of regular expressions and test them against a fixed string? I tried to play with pattern space, hold space, with no success. It just seems impossible to use them (which would be the closest to "variables") in search commands.

I know sed is Turing complete, but using it that way would maybe require to implement a regexp engine from scratch?

Thanks!

After a long time I'm in a situation where I sometimes work on a temporary system without my individual setup. Now whenever I might add a new custom (nushell) command that abstracts the usage of CLI tools, I think about the loss of muscle memory/knowledge for these tools and how much time I waste looking them up without my individual setup. No, that's not a huge amount of time, but just out of curiosity I'd like to know how I can minimize this problem as much as possible.

Do you have some tips and solutions to handle this dilemma? I try to shadow and wrap existing commands, whenever it's possible, but that's often not the case. Abbreviations in fish are optimal for this problem in some cases, but I don't think going back to fish as my main shell for this single reason would be worth it.

The document itself is paywalled like all the POSIX specifications, so here are some highlights courtesy of some comments at HackerNews, especially from a-french-anon.

• readlink and realpath
• find -print0, xargs -0 and read -d
• find -iname
• sed -E
• set -o pipefail
• $' ' strings