Ubuntu – Unsure of grep output because of bash wildcards

bashgrep

I am trying to get a better understanding of bash commands.

ls /usr/include/ | grep \.h

It is supposed to list all the files ending in .h (C libraries) but it outputs more than expected.

thread_db .h

uchar .h

netash

If someone could also tell me how to bold the .h in the question without separating it from the rest of the name with a space, i would appriciate it.

Best Answer

In grep, your pattern is matching .h (any character followed by h) anywhere in the line, not just at the end.

You basically have two problems:

Quoting/escaping issue
Regex pattern issue

Explanations:

You have escaped . using \. and have not used any quotes or another \, so the escaping would escape the shell, and grep would get the Regex pattern as .h, in Regex term which means any character followed by a h. Your target is to make grep treat the . literal, so you need to quote or add another \ like:
```
'\.h'
\\.h
```
Now the second problem, in regex, the end of a line is expressed by the quantifier $, so as you need to match the .h at the end of the line:
```
'\.h$'
```

So, together the correct usage would be:

ls /usr/include/ | grep '\.h$'

Now the most important thing, Don't parse ls.

What you are doing can be easily and efficiently done by basic shell globbing:

ls /usr/include/*.h

Related Solutions

Ubuntu – How to evaluate grep result in bash

You can make use of grep's return status.

systemctl status asd.service | grep 'active' \
    && status=active \
    || status=not_active

if [ "$status" == "active" ]; then
    [...]
fi

or even easier:

test $(systemctl status asd.service | grep 'active') \
    && echo "$SERVICE was active"

or if you prefer if:

if $(systemctl status asd.service | grep 'active'); then
    echo "$SERVICE was active"
fi

Anyways, take care about the keywords inactive, not active, active (exited) or alike. This will also match your grep statement. See the comments. Thanks @ Terrance for the hint.

Update:

No need for grep. systemctl has the command is-active included.

systemctl -q is-active asd.service \
    && echo "$SERVICE was active"

or:

if systemctl -q is-active asd.service; then
    echo "is active";
fi

Ubuntu – Shell script to skip PPA if installed

That is a bash function, and to pass arguments to bash functions, you don't need (). Also, the function adds the ppa: prefix to its arguments, so just this would do:

add_ppa otto-kesselgulasch/gimp-edge

Additionally, the function supports multiple arguments, so you can run it for multiple PPAs:

add_ppa otto-kesselgulasch/gimp-edge foo/bar a/b

Given that you have put the function in a script, you should either:

source it as Zanna suggests to get the function in your shell and call the function, or

just use the contents of the function as the script:

#! /bin/bash
for i in "$@"; do
  if grep -Rq "^deb.*$i" /etc/apt/sources.list.d/*.list
  then
    echo "Adding ppa:$i"
    sudo add-apt-repository -y ppa:$i
  else
    echo "ppa:$i already exists"
  fi
done

And the call the script with the ppa name:

ppa otto-kesselgulasch/gimp-edge

Best Answer

Related Solutions

Ubuntu – How to evaluate grep result in bash

Update:

Ubuntu – Shell script to skip PPA if installed

Related Question