插入符号正则表达式在 mawk 中不产生 output

Question

I am trying to print all files in /usr/bin/ where the filename starts with a v . This works,

ls -lA /usr/bin/ | awk '{print $9}' | grep ^v

Surprisingly, this returns no output,

ls -lA /usr/bin/ | awk '/^v/ {print $9}' ls -lA /usr/bin/ | awk '/^v/ {print $9}' .

I don't understand the difference. I am running Ubuntu 21.10 with awk -W version saying that it is on 1.3.4 20200120 .

Edit: I understand that awk may not be the best way to accomplish what I am wanting to do here. But, this is an exercise in learning awk by testing my understanding via comparing it to the real output.

Answer 1

The difference between the two pipelines is that the first outputs the 9th column and then check to see if that starts with a v the second checks to see if the line starts with a v , change the second to:

$ ls -lA /usr/bin/ | awk '$9 ~ /^v/ {print $9}'

When writing:

/pattern/ { ... }

it's the same as writing

$0 ~ /pattern/ { ... }

but in your case you want to compare the 9th column, so write that instead.

---

But you really don't want to create a pipeline for this, and what would happen if your files contain a space?

You can consider using find or globs instead:

$ printf '%s\n' /usr/bin/v*
/usr/bin/vi
/usr/bin/view
...

or

$ find /usr/bin -name 'v*' -print
/usr/bin/vi
/usr/bin/view
...