CODEWITHSUNDEEP
shelldata-driven
thoni56
thoni56

Reputation: 3335

Datadriven shell programming? Suggestions, please

I'd like to convert my shell script to use a datadriven approach. But since there are no "tables" type values in any shell (that I know of), what are suggested alternative ways to do this?

What I'm looking for is solutions that would allow one to do things like:

animals = [['horse', 300 'brown'],
           ['cat', 3, 'black'],
           ['elephant', 3000, 'grey'],
           ['mouse', 0.3, 'grey']]
for a in animals ; do
  echo "A typical $a[1] is $a[3] and weighs about $a[2] kilograms."
done

More precisely, I'd like to try a number of commands and see if one of them is available, and then send arguments to it:

commands = [['c1', '-m', '-i'],
            ['c2', '-message', '-icon'],
            ['c3', '/m', '/i']]
for c in commands ; do
  if exists c[1] ; then
    command = c[1]
    message_option = c[2]
    icon_option = c[3]
    break;
  fi
done
$command $message_option "message" $icon_option icon

Upvotes: 2

Views: 93

Answers (3)

Jens
Jens

Reputation: 72707

No bashisms needed. This can be neatly solved with a here-document read by a while read loop:

#!/bin/sh
while read animal weigth colour; do
  printf '%s\n' "A typical $animal is $colour and weighs about $weight kilos."
done << EOF
horse 300 brown
cat 3 black
elephant 3000 grey
mouse 0.3 grey
EOF

Observe how this refers to the elements by name, not cryptic indexing with 1, 2, 3. It doesn't fork/exec any external commands and beats the 3 awks in the loop body seen in another answer hands down.

Upvotes: 4

Inian
Inian

Reputation: 85800

You can define and use associative-arrays in bash for your requirement.

#!/bin/bash

# declaring the Associative array
declare -a animals

animals[0]="'horse':300:'brown'"
animals[1]="'cat':3:'black'"
animals[2]="'elephant':3000:'grey'"
animals[3]="'mouse':0.3:'grey'"

for animal in "${animals[@]}"
do
    myArray=(${animal//:/ })
    printf "A typical "${myArray[0]}" is "${myArray[2]}" and weighs about "${myArray[1]}" kilograms.\n"
done

The only tricky part in the above is parameter-expansion of type

${parameter/pattern/string}
          The pattern is expanded to produce a pattern just as in filename expansion. Parameter is expanded and the longest match of pattern against its value is replaced with string. 
If pattern begins with ‘/’, all matches of pattern are replaced with string. Normally only the first match is replaced.

So ideally the string 'horse':300:'brown' is split as individual elements and stored in the array myArray which is later used to access individual elements in a C-style loop.

Upvotes: 2

Chem-man17
Chem-man17

Reputation: 1770

Try this?

cat file
'horse', 300, 'brown'
'cat', 3, 'black'
'elephant', 3000, 'grey'
'mouse', 0.3, 'grey'

for i in {1..4} ; 
do 
    animal=$(awk -F, -v var="$i" 'NR== var {print $1}' file) 
    weight=$(awk -F, -v var="$i" 'NR== var {print $2}' file) 
    colour=$(awk -F, -v var="$i" 'NR== var {print $3}' file) 
    echo "A typical "$animal" is "$colour" and weighs about "$weight" kilos." 
done

Output-

A typical 'horse' is 'brown' and weighs about  300 kilos.
A typical 'cat' is  'black' and weighs about  3 kilos.
A typical 'elephant' is  'grey' and weighs about  3000 kilos.
A typical 'mouse' is  'grey' and weighs about  0.3 kilos.

Upvotes: 0

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