» CS 330 Lecture 2 – Hello, Shell

CS 330 Lecture 2 – Hello, Shell

January 28, 2015 by Chris Johnson. Filed under cs330, lectures, spring 2015.

Agenda

what ?s
some shell exercises
tell me something you know about the shell
the UNIX way

TODO

Set your homework repository.
Read Shell Programming with Bash.
1/4 sheet: share 3-4 questions or observations about shells or Bitbucket. I offer you some optional challenge problems, which may be solved with one line of shell code:
- You are a web server administrator. Make all files in /var/www (even those in subdirectories) readable to others. If the files are executable by the user/owner, also make them executable by others.
- Read a file of text, determine the n most frequently used words, and print out a sorted list of those words along with their frequencies.
Optional: check out Zsh.

Questions

What’s the purpose of the shell? What’s something you might want to do with a shell script that isn’t as easy in another language?
Does the shell have a means of persisting data?
Does the shell support expressions?
Does the shell support types?
Does the shell have a mechanism for abstracting code?
Does the shell have a mechanism for passing data around?
Does the shell have a standard library?
How are errors handled?
What’s different about a shell script vs. C code?

Code

fixext

#!/usr/bin/env zsh

newext=$1
shift

for i in $@; do
  yes | mv $i ${i:r}.$newext
done

safe_rm

#!/usr/bin/env zsh

trash=$HOME/.junkies

mkdir -p $trash
for i in $@; do
  mv $i $trash/${i:t}.$RANDOM
done

bigs

#!/bin/sh

du | sort -nr | head -n 20

massmail

#!/usr/bin/env zsh

for i in $(cut -f2 -d, grades.csv | sed 1d); do
  echo "Delete this email." | mail -s "[CS 330] Real Good Deal on Chronometers" $i@uwec.edu
done

dirdiff

#!/usr/bin/env zsh

d1=$1
d2=$2

for i in $d1/*; do
  basename=${i:t}
  if [[ ! -e $d2/$basename ]]; then
    echo "No $basename in $d2!"
  elif [[ -d $i ]]; then
    $0 $i $d2/$basename
  else
    diff $i $d2/$basename >/dev/null
    if [[ $? -ne 0 ]]; then
      echo "Files $i and $d2/$basename differ."
    fi
  fi
done

Haiku

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