16.9. Miscellaneous Commands (Revision #1)

Command that fit in no special category

jot, seq

These utilities emit a sequence of integers, with a user-selectable increment.

The default separator character between each integer is a newline, but this can be changed with the -s option.

bash$ seq 5
1
2
3
4
5

bash$ seq -s : 5
1:2:3:4:5

Both  jot  and seq come in  handy in a for loop.

Example 16-54. Using seq to generate loop arguments

#!/bin/bash
# Using "seq"

echo

for a in `seq 80`  # or   for a in $( seq 80 )
# Same as   for a in 1 2 3 4 5 ... 80   (saves much typing!).
# May also use 'jot' (if present on system).
do
echo -n "$a "
done      # 1 2 3 4 5 ... 80
# Example of using the output of a command to generate
# the [list] in a "for" loop.

echo; echo

COUNT=80  # Yes, 'seq' also accepts a replaceable parameter.

for a in `seq $COUNT`  # or   for a in $( seq $COUNT )
do
echo -n "$a "
done      # 1 2 3 4 5 ... 80

echo; echo

BEGIN=75
END=80

for a in `seq $BEGIN $END`
#  Giving "seq" two arguments starts the count at the first one,
#+ and continues until it reaches the second.
do
echo -n "$a "
done      # 75 76 77 78 79 80

echo; echo

BEGIN=45
INTERVAL=5
END=80

for a in `seq $BEGIN $INTERVAL $END`
#  Giving "seq" three arguments starts the count at the first one,
#+ uses the second for a step interval,
#+ and continues until it reaches the third.
do
echo -n "$a "
done      # 45 50 55 60 65 70 75 80

echo; echo

exit 0

A simpler example:

#  Create a set of 10 files,
#+ named file.1, file.2 . . . file.10.
COUNT=10
PREFIX=file

for filename in `seq $COUNT`
do
touch $PREFIX.$filename
#  Or, can do other operations,
#+ such as rm, grep, etc.
done

Example 16-55. Letter Count"

#!/bin/bash
# letter-count.sh: Counting letter occurrences in a text file.
# Written by Stefano Palmeri.
# Used in ABS Guide with permission.
# Slightly modified by document author.

MINARGS=2          # Script requires at least two arguments.
E_BADARGS=65
FILE=$1

let LETTERS=$#-1   # How many letters specified (as command-line args).
           # (Subtract 1 from number of command-line args.)

show_help(){
   echo
       echo Usage: `basename $0` file letters  
       echo Note: `basename $0` arguments are case sensitive.
       echo Example: `basename $0` foobar.txt G n U L i N U x.
   echo
}

# Checks number of arguments.
if [ $# -lt $MINARGS ]; then
echo
echo "Not enough arguments."
echo
show_help
exit $E_BADARGS
fi  


# Checks if file exists.
if [ ! -f $FILE ]; then
echo "File \"$FILE\" does not exist."
exit $E_BADARGS
fi

# Counts letter occurrences .
for n in `seq $LETTERS`; do
  shift
  if [[ `echo -n "$1" | wc -c` -eq 1 ]]; then             #  Checks arg.
     echo "$1" -\> `cat $FILE | tr -cd  "$1" | wc -c` #  Counting.
  else
     echo "$1 is not a  single char."
  fi  
done

exit $?

#  This script has exactly the same functionality as letter-count2.sh,
#+ but executes faster.
#  Why?

    Somewhat more capable than seq, jot is a classic UNIX utility that is not normally included in a standard Linux distro. However, the source rpm is available for download from the MIT repository.

Unlike seq, jot can generate a sequence of random numbers, using the -r option.

bash$ jot -r 3 999
1069
 1272
 1428

getopt

The getopt command parses command-line options preceded by a dash. This external command corresponds to the getopts Bash builtin. Using getopt permits handling long options by means of the -l flag, and this also allows parameter reshuffling.

Example 16-56. Using getopt to parse command-line options

#!/bin/bash
# Using getopt

# Try the following when invoking this script:
#   sh ex33a.sh -a
#   sh ex33a.sh -abc
#   sh ex33a.sh -a -b -c
#   sh ex33a.sh -d
#   sh ex33a.sh -dXYZ
#   sh ex33a.sh -d XYZ
#   sh ex33a.sh -abcd
#   sh ex33a.sh -abcdZ
#   sh ex33a.sh -z
#   sh ex33a.sh a
# Explain the results of each of the above.

E_OPTERR=65

if [ "$#" -eq 0 ]
then   # Script needs at least one command-line argument.
  echo "Usage $0 -[options a,b,c]"
  exit $E_OPTERR
fi  

set -- `getopt "abcd:" "$@"`
# Sets positional parameters to command-line arguments.
# What happens if you use "$*" instead of "$@"?

while [ ! -z "$1" ]
do
  case "$1" in
    -a) echo "Option \"a\"";;
    -b) echo "Option \"b\"";;
    -c) echo "Option \"c\"";;
    -d) echo "Option \"d\" $2";;
     *) break;;
  esac

  shift
done

#  It is usually better to use the 'getopts' builtin in a script.
#  See "ex33.sh."

exit 0