Week 6, Intro to Unix lab 2016

05 Apr 2016

Content

Recap homework
- rev - GNU specific
- bc, cut -c
- sed 's/(.*)([0-9]*) ([a-zA-Z]*)/\3 \2\1/'
- printf
- run commands in batch after you ssh to remote computer e.g.
  - ssh login@computer 'your_first_command; your_other | piped_command'
- grep -E does not use basic regular expressions;-)
  - What are the differences?
Recap
- join, tee, tail, pwd, pg, less, more, head, chmod, chown, tr, cut, wc, strings, cat
presentation/todos - diff, comm, paste, split
sed regexp continuation
Additional program flow commands
- while, read, if

(1 point) Write a script nl_4digits.sh which uses a while and read commands to reading a standard input and inserting a number at the beginning of line together with a double colon.

# Example input:
Hi Jack,
how are you?

# Example output:
0001: Hi Jack,
0002: how are you?

(1 point) Write a script palindrome.sh [argument] which takes as argument either file name or -.
- If filename is provided it process lines from file. If - is provided it process lines from stdin.
- For each line it decides whether it is a palindrome. If it is not palindrome it skips the line otherwise it prints the palindrome to standard output.
(1 point) Write a script evener.sh which keeps only even lines in the input file
- hints: seq, seq -n, sed 'command1;command2;command3' file

# Example
$ seq 11 > test_input
$ evener.sh test_input
$ cat test_input
2
4
6
8
10