linux tools shell script.. computer science
Singpran
ShellProgramming-Arrays51.pptARRAYS
- Array is a variable which contains multiple values may be of same type or different type since by default in shell script everything is treated as a string.
- An array is zero-based ie indexing start with 0.
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HOW TO DECLARE ARRAY IN SHELL SCRIPTING?
1. Indirect Declaration
Assign a value in a particular index of Array Variable. No need to first declare
ARRAYNAME[INDEXNR]=value
2. Explicit Declaration
declare -a ARRAYNAME
3. Compound Assignment
ARRAYNAME=(value1 value2 .... valueN)
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ARRAYS IN BASH
- bash has two types of arrays: one-dimensional indexed arrays and associative arrays •
- Any variable can be used as a 1D array – Identified as var[index]
$x=24
$ echo ${x[0]}
- Indexed arrays
• Index array need not be declared though they can be using the command declare -a
• You can also declare arrays of any size by
declare -a color[3]
with the elements indexed from 0 to 2 –
In reality, the index above is ignored
– You can simply add more elements to it by assigning an element with a new index
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ACCESSED BY AN INDEX
– Index starts at 0
– Index can be any positive integer, up to 599147937791
– Arithmetic expressions are supported in index
• Values are assigned by
var[index]=value
• Examples
color[1]="red"
color[2]="green"
color[0]="blue"
– Values need not be assigned in any specific order
Another way to assign values, known as compound statement, is
color=([2]=green [1]=red [0]=blue)
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If you specify the elements in order, you can specify them as
color=(red blue green)
• The above values can be accessed by
for i in 0 1 2
do
echo ${color[$i]}
done
– You must use the curly braces to access array elements; otherwise, you’ll just get the first array element and the subscript
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IFS: internal field separator
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TO COUNT LENGTH OF ARRAY
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COLOR=(RED BLUE GREEN)
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COLOR=(RED BLUE GREEN)
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COLOR=(RED BLUE GREEN)
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The contents of the colors array is not change, only the output
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BASH ASSOCIATIVE ARRAY EXAMPLES
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(foo=bar baz=quux corge=grault)
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QUOTING KEYS
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$ k=plugh
$ MYMAP['$K']=xyzzy
$ echo ${MYMAP[plugh]}
$ echo ${MYMAP['$K']}
xyzzy
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ASSOCIATIVEARRAYS
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Use:
printf instead of print
([apple red] [banana yellow] [grape purple])
LOOPING
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Use double quotation “
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ECHO
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${MYMAP[${KEYS[$I]}]}
KEYS=(“foo a” “baz b)
SCOPE
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