Everyday Shell Scripts

• Rename the extensions of all files,

  for FILE in *.foo ; 
  do NEWFILE=`echo $FILE | sed 's/.foo/.bar/g'` ;
   mv "$FILE" $NEWFILE ; 
  done

• Test if a variable is set (pay attention to the space, they can't be eliminated),

  if [ ! -z "$var" ]; then
    echo "var exists"
  fi

• Test if a file exists,

  if [ -f "$file" ]; then
    echo "file exists"
  fi

• Copy one file to the clipboard (install xclip first)

  cat file | xclip -selection c

• Paste clipboard to a file

  xclip -o > file

• Define a function

  foo(){
    echo "FUNCTION"
  }
  fun=$(foo)
  

• The most recent foreground pipeline exit status: $?

  if [ $? -eq -1 ]
    then
    exit 1
  fi 

• Several ways of for loop controlled by a var

  for I in {1..10}; do echo $I; done
  for I in 1 2 3 4 5 6 7 8 9 10; do echo $I; done
  for I in $(seq 1 10); do echo $I; done
  for ((I=1; I <= 10 ; I++)); do echo $I; done

• Generate ticks in (-4pi, 4pi):

  for i in $(seq -4 4); do b=`echo "$i * 3.14159" | bc`; echo -ne $b","; done; 

  This is useful for PGFplots for trigonometric ticks,

  xtick={-12.56636,-9.42477,-6.28318,-3.14159,0,
  3.14159,6.28318,9.42477,12.56636},
  xticklabels={
          $-4\pi$, $-3\pi$, $-2\pi$, $-\pi$, $0$,
          $\pi$, $2\pi$, $3\pi$, $4\pi$
   }

• Convert all jpeg files and save them as png files.

  for file in *.jpg;do 
    newfile=`echo $file | sed 's/.jpg/.png/g'`;
    gm convert -quality 60 $file $newfile;
  done

• Compress all jpeg files.

  mkdir new
  for file in *.jpg;do 
    newfile="new/$file";
    gm convert -quality 60 $file $newfile;
  done