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Operating Systems Linux Fedora Help with controlling string elements
# 1  
Old 03-13-2011
Help with controlling string elements
Hi All,

I have a general difficulty in understanding how to control single elements within a string. An example,



Code:
XYZ1234      ABCD5678

My expected output is :



Code:
ABCD1234     XYZ5678  (swapping subset of string elements of choice)
XYZ37            ACBD1214 (making calculations using string elements)

,etc

Could someone illuminate on such problems please.

Thanks in advance Smilie

PS: I'm a beginner to UNIX Image
# 2  
Old 03-13-2011
Read the following link about string operators and pattern matching operator :
String Operators (Learning the Korn Shell, 2nd Edition)

Then understand and reproduce the given examples.

Code:
$ a=/users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

Code:
$ echo $a
/users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

Code:
$ echo ${a#*/}
users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

Code:
$ echo ${a##*/}
1900_CDCRM_CBF71_13022010_13022010.txt

Code:
$ echo ${a%_*}
/users/home/ctsgnb/1900_CDCRM_CBF71_13022010

Code:
$ echo ${a%%_*}
/users/home/ctsgnb/1900

Code:
$ echo ${a%.*}
/users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010

Code:
$ echo ${a#?}
users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

Code:
$ echo ${a##?}
users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

Code:
$ echo ${a%?}
/users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.tx

Code:
$ echo ${a%%?}
/users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.tx

---------- Post updated at 10:42 PM ---------- Previous update was at 10:23 PM ----------

You also have to understand meaning of meta character in regular expression see
Syntax of sed Commands (sed & awk, Second Edition)

---------- Post updated at 10:43 PM ---------- Previous update was at 10:42 PM ----------

some examples :
Code:
[ctsgnb@shell ~]$ echo $a
/users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/_/#/'
/users/home/ctsgnb/1900#CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/_/#/g'
/users/home/ctsgnb/1900#CDCRM#CBF71#13022010#13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/_/#/2'
/users/home/ctsgnb/1900_CDCRM#CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/_/#/3'
/users/home/ctsgnb/1900_CDCRM_CBF71#13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/ctsgnb/toto/'
/users/home/toto/1900_CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/.*/# &/'
# /users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/\(.*\)ctsgnb/ctsgnb\1/'
ctsgnb/users/home//1900_CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/.*\(ctsgnb\)/\1/'
ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$

This User Gave Thanks to ctsgnb For This Post:
pawannoel
# 3  
Old 03-13-2011
Thank you very much ...

Its really exciting and your examples are helping me understand it nicely

If you think any other stuff is basic and will fit my level please let me know.

Thanks again and have a nice week ahead Smilie

---------- Post updated at 06:22 PM ---------- Previous update was at 06:13 PM ----------

Could you please comment on these last 3 sed command examples u sent,

didnt really get how they work !!

Cheers Smilie

Code:
[ctsgnb@shell ~]$ echo $a | sed 's/.*/# &/'
# /users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/\(.*\)ctsgnb/ctsgnb\1/'
ctsgnb/users/home//1900_CDCRM_CBF71_13022010_13022010.txt
[ctsgnb@shell ~]$ echo $a | sed 's/.*\(ctsgnb\)/\1/'
ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

# 4  
Old 03-13-2011
Code:
ctsgnb@shell ~]$ echo $a | sed 's/.*/# &/'
# /users/home/ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

replace all characters ('.' is any char, '*' is zero or more) with
a hash sign, space and whatever you captured ('&') as .*

Code:
[ctsgnb@shell ~]$ echo $a | sed 's/\(.*\)ctsgnb/ctsgnb\1/'
ctsgnb/users/home//1900_CDCRM_CBF71_13022010_13022010.txt

capture ('\(' and '\)' define the beg and end) any characters immediately before 'ctsgnb' string and
replace captured string and "ctsgnb" with "ctsgnb" concatenated with whatever was captured

Code:
[ctsgnb@shell ~]$ echo $a | sed 's/.*\(ctsgnb\)/\1/'
ctsgnb/1900_CDCRM_CBF71_13022010_13022010.txt

replace any chars before string "ctsgnb" and the string itself, with what was captured.
Only pattern that could match the capture is "ctsgnb" string.
Same as
Code:
echo $a | sed 's/.*ctsgnb/ctsgnb/'

without an instructional use of capturing with parentheses Smilie
# 5  
Old 03-14-2011
@mirni :

Yes, i used \( ...\) and \1 just for demonstration purpose.

@pawannoel :

when using
Code:
s/.../...&.../

the & refer to what has been matched in the first /.../ part (in red)

You could also play with the cut command and its options it may also be usefull in string manipulation in some case.
Code:
man cut

# 6  
Old 03-14-2011
@pawannoel:
This kind of substitution may come in handy also:
Code:
  $ var=kofoo23.txt
 $ echo ${var/foo/bar}
kobar23.txt

Can also be done with nested vars:
Code:
  $ str=BAR
  $ echo ${var/foo/$str}
koBAR23.txt

For details look at 'man bash' , and search for 'parameter expansion'

@ctsgnb:
Which shell (and version) are you using? I can't seem to find the
echo ${a##?}
echo ${a#?}
expansions in 'man bash' on my system (GNU bash, version 4.1.5(1)-release (i486-pc-linux-gnu)), although it seems to work on CL. What do these do?
# 7  
Old 03-14-2011
That was ksh on a FreeBSD (not sure about the version, but it i think it was not a ksh93) the ? is expanded by the shell as matching any single character (but 1 and only 1) similar to (but not exactly same as) the dot in regex

---------- Post updated at 11:53 AM ---------- Previous update was at 11:27 AM ----------

@pawannoel :

still for demo purpose :

Code:
# echo "XYZ1234      ABCD5678"
XYZ1234      ABCD5678
# echo "XYZ1234      ABCD5678" | sed 's/^.../ABCD/;s/ABCD/XYZ/2'
ABCD1234      XYZ5678
# echo "XYZ1234      ABCD5678" | sed 's/^\(...\)\([^A-Z]*\)\(....\)\(.*\)$/\3\2\1\4/'
ABCD1234      XYZ5678
# echo "XYZ1234      ABCD5678" | sed 's/^\([A-Z]*\)\([0-9]*\)\([[:blank:]]*\)\([A-Z]*\)\([0-9]*\)$/\4\2\3\1\5/'
ABCD1234      XYZ5678
#

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