Viewing Files

Once you can find files, the next skill is reading them — especially logs, without opening an editor.

cat and less #

cat dumps a whole file to the screen — fine for something short. For anything long, less lets you scroll one screen at a time instead of flooding your terminal.

cat notes.txt
less server.log

head and tail #

head server.log          # first 10 lines
head -n 20 server.log     # first 20 lines
tail server.log           # last 10 lines
tail -n 20 server.log     # last 20 lines

grep — finding a needle in a log file #

If server.log contains a mix of INFO and ERROR lines, this pulls out only the errors:

grep ERROR server.log
grep -i error server.log     # case-insensitive
grep -r "ERROR" logs/        # search every file under logs/