How do I display all the characters between two specific strings?

The question is only interesting if the delimiters are not necessarily on the same line. It can be done several ways (even with sed), but awk is more flexible:

    #!/bin/sh
    awk '
    BEGIN { found = 0; }
    /xxx/ {
        if (!found) {
            found = 1;
            $0 = substr($0, index($0, "xxx") + 3);
        }
    }
    /yyy/ {
        if (found) {
            found = 2;
            $0 = substr($0, 0, index($0, "yyy") - 1);
        }
    }   
        { if (found) {
            print;
            if (found == 2)
                found = 0;
        }
    }
    '

This is tested lightly for the cases where at most one substring is on a line, using this data:

    this is xxx yy
    first
    second yyy

    xxx.x
    yyy

    xxx#yyy

and this output (script is "foo", data is "foo.in"):

    $ cat foo.in|./foo
     yy
    first
    second 
    .x

    #

The way it works, is that the input data is in $0, and awk matches the patterns xxx and yyy in sequence, allowing more than one thing to change $0 on its way to the last step, where it is printed.

By the way, this example would not work for

xxxxHelloyyyxxxWorldyyy

since it checks only the first match. The Perl script will give different results, since it uses a greedy match rather than the index/substr which I used in the awk example. Perl, of course, can do the same -- with a script.

Awk (like Perl) is free-format, so one could express the command as something like

awk 'BEGIN{found=0;}/xxx/{if(!found){found=1;$0=substr($0,index($0, "xxx")+3);}}/yyy/{if(found){found=2;$0=substr($0,0,index($0,"yyy")-1);}}{ if(found){print;if(found==2)found=0;}}'

but that is rarely done, except for the sake of example. Likewise, sed scripts (line-oriented), can be combined into a single line with some restrictions. Again, complex scripts in sed are rarely dealt with in that manner. Rather, they are treated like real programs (see example).

Further reading:

• AWK Language Programming, Edition 1.0
• mawk - pattern scanning and text processing language
• Unix Sed Tutorial: 6 Examples for Sed Branching Operation

This should do what you are trying to do :

sed -e 's/xxx\(.*\)yyy/\1/'

This assumes both delimiter strings are on the same line

A solution that also works when xxxand yyy is not on the same line: cat /tmp/xxx-to-yyy| perl -ne '(/xxx/../yyy/) && print' | perl -pe 's/.*(xxx.*)/$1/' | perl -pe 's/(.*yyy).*/$1/'

Not exactly pretty...

The -e switch to perl is just to give the script on the command line. The -n and -p makes it loop over the input lines, with -p they are printed after the script, with -n they aren't. So basically this just sends the file through three perl loops.

.. is a range operator, that returns false until the left condition returns true, and false after the right condition returns true, so the first loop cut down the file to the lines between the two strings (both included. The last two perl commands remove the text before xxx and after yyy.

Here is a solution with python :

import sys
import re
F=open(sys.argv[1])
text=F.read()
reg=re.compile("xxx((?:.|\n)*)yyy")
for match in reg.finditer(text):
    print match.groups()[0]

Save this script as a file "post.py" and launch it with:

python post.py your_file_to_search_in.txt

The script compiles a regular expression and print all occurences found in the text of the file.

(?:.|\n) is a non capturing group matching any character including newline

Edit : solution improved thanks to 1_CR tips :

import sys
import re
F=open(sys.argv[1])
text=F.read()
reg=re.compile(r'xxx(.*)yyy',re.DOTALL)
for match in reg.finditer(text):
    print match.groups()[0]