bash_scripting [Whizzbang Tech Stuff]

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======Bash Scripting======
======Conditionals======
  * The special variable ''$?'' has the exit/return value of the last program/command that ran.

<code bash>
if [ $? -eq 0 ]; then
    echo "All is well."
    exit 0
elif [ $? -eq 1 ]; then 
    echo "Doh!"
    exit 1
else
   echo "Really?!"
   exit 2
fi
</code>

===One line if statement===
<code bash>
if [$? -eq 0]; then echo "OK"; else echo "Error"; fi
</code>

======Iteration======
===for loop===
<code bash>
for i in alpha beta gamma
do
    printf "$i\n"
done

a=alpha
b=beta
c=gamma

for j in "$a" "$b" "$c"; do
    printf "$j\n"
done
</code>

<code bash>
for i in $( ls ); do
  echo item: $i
done

LIST="$(ls *.html)"
for i in "$LIST"; do
   echo $1
done
</code>

===while loop===
<code bash>
COUNTER=0

while [  $COUNTER -lt 10 ]; do
  echo The counter is $COUNTER
  let COUNTER=COUNTER+1 
done
</code>

======Command Substitution/Interpolation======
  * Command substitution will run the specified command and replace the command with the output from the command in the location where it is specified as part of input to some other command.
<code>
$(<command expression>)
</code>
<code>
text=$(cat alpha.txt)
</code>
<code>
`<command expression>`
</code>

======File Manipulation======
==Delete a file if it exists.==
<code bash>
[[ -f "$file" ]] && rm -f "$file"
</code>

======File I/O======

===Read a text file line by line.===
<code bash>
#!/bin/bash
while read line
do
    name=$line
    echo "Text read from file - $name"
done < $1
</code>

===Read each line of a file as a CSV record.===
<code bash>
while IFS=, read col1 col2
do
    echo "I got:$col1|$col2"
done < myfile.csv
</code>

======Resources======
  * [[http://wiki.bash-hackers.org/|The Bash Hackers Wiki]]