Answer:

Suppose you want to grep a specific code from files with a specific file extension, you can try

# grep -r --include \*.php 'error_log(' .

Answer:

If you want to tail a remote file over ssh, you can use

# ssh -t remote-server "tail -f /var/log/log.txt"

Answer:

You should always start your bash shell script with the line set -eu

The meaning is:

1. -e: cause the script to exit if an error
2. -u: cause the script to exit if any variable is not set

Answer:

You can list all system's currently installed locales via the command: locale -a

Answer:

If you have a list of IPs and need to resolve to the hostname(via reverse DNS lookup), you can use the following command:

cat ip_addresses.txt | xargs -n 1 -P 100  -i dig -x {} +short

Answer:

You can use the following command to find files and tar them together

# find . -type f -print0 | tar -czvf backup.tgz --null -T -

Answer:

"git log" will not show the changed file in the output, to show it, use

# git log --stat

Answer:

If you want to change the case of filename of all files in a directory, e.g. change to all UPPER case, you can use:

# rename 'y/a-z/A-Z/' *

Answer:

When you've installed imagemagick, you can mass resize images using the "mogrify" command, e.g.

# mogrify -resize 320x240 *.jpg

Answer:

If you know Perl well, there is no need to use awk to do string processing such as string splitting, it is easy with Perl also, e.g.

# echo "foo,bar,k3"  | perl -F',' -lane 'print $F[1]'
bar