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Top Forums Shell Programming and Scripting Drop common lines at head/tail of a large set of files Post 302316903 by dobryden on Sunday 17th of May 2009 07:26:17 AM
Old 05-17-2009
Drop common lines at head/tail of a large set of files

Hi! I have a large set of pairs of text files (each pair in their own subdirectory) and each pair shares head/tail (a couple of first and last lines) but differs in the middle part. I need to delete the heads/tails and keep only the middle portions in which they differ. The lengths of heads/tails are not the same (in terms of number of lines) for different pairs. Do you know an easy way to delete all the heads (tails) at once for all the files? Thanks a lot in advance!
 

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GIT-SHOW-REF(1) 						    Git Manual							   GIT-SHOW-REF(1)

NAME
       git-show-ref - List references in a local repository

SYNOPSIS
       git show-ref [-q|--quiet] [--verify] [--head] [-d|--dereference]
		    [-s|--hash[=<n>]] [--abbrev[=<n>]] [--tags]
		    [--heads] [--] [<pattern>...]
       git show-ref --exclude-existing[=<pattern>]

DESCRIPTION
       Displays references available in a local repository along with the associated commit IDs. Results can be filtered using a pattern and tags
       can be dereferenced into object IDs. Additionally, it can be used to test whether a particular ref exists.

       By default, shows the tags, heads, and remote refs.

       The --exclude-existing form is a filter that does the inverse. It reads refs from stdin, one ref per line, and shows those that don't exist
       in the local repository.

       Use of this utility is encouraged in favor of directly accessing files under the .git directory.

OPTIONS
       --head
	   Show the HEAD reference, even if it would normally be filtered out.

       --tags, --heads
	   Limit to "refs/heads" and "refs/tags", respectively. These options are not mutually exclusive; when given both, references stored in
	   "refs/heads" and "refs/tags" are displayed.

       -d, --dereference
	   Dereference tags into object IDs as well. They will be shown with "^{}" appended.

       -s, --hash[=<n>]
	   Only show the SHA-1 hash, not the reference name. When combined with --dereference the dereferenced tag will still be shown after the
	   SHA-1.

       --verify
	   Enable stricter reference checking by requiring an exact ref path. Aside from returning an error code of 1, it will also print an error
	   message if --quiet was not specified.

       --abbrev[=<n>]
	   Abbreviate the object name. When using --hash, you do not have to say --hash --abbrev; --hash=n would do.

       -q, --quiet
	   Do not print any results to stdout. When combined with --verify this can be used to silently check if a reference exists.

       --exclude-existing[=<pattern>]
	   Make git show-ref act as a filter that reads refs from stdin of the form "^(?:<anything>s)?<refname>(?:^{})?$" and performs the
	   following actions on each: (1) strip "^{}" at the end of line if any; (2) ignore if pattern is provided and does not head-match
	   refname; (3) warn if refname is not a well-formed refname and skip; (4) ignore if refname is a ref that exists in the local repository;
	   (5) otherwise output the line.

       <pattern>...
	   Show references matching one or more patterns. Patterns are matched from the end of the full name, and only complete parts are matched,
	   e.g.  master matches refs/heads/master, refs/remotes/origin/master, refs/tags/jedi/master but not refs/heads/mymaster or
	   refs/remotes/master/jedi.

OUTPUT
       The output is in the format: <SHA-1 ID> <space> <reference name>.

	   $ git show-ref --head --dereference
	   832e76a9899f560a90ffd62ae2ce83bbeff58f54 HEAD
	   832e76a9899f560a90ffd62ae2ce83bbeff58f54 refs/heads/master
	   832e76a9899f560a90ffd62ae2ce83bbeff58f54 refs/heads/origin
	   3521017556c5de4159da4615a39fa4d5d2c279b5 refs/tags/v0.99.9c
	   6ddc0964034342519a87fe013781abf31c6db6ad refs/tags/v0.99.9c^{}
	   055e4ae3ae6eb344cbabf2a5256a49ea66040131 refs/tags/v1.0rc4
	   423325a2d24638ddcc82ce47be5e40be550f4507 refs/tags/v1.0rc4^{}
	   ...

       When using --hash (and not --dereference) the output format is: <SHA-1 ID>

	   $ git show-ref --heads --hash
	   2e3ba0114a1f52b47df29743d6915d056be13278
	   185008ae97960c8d551adcd9e23565194651b5d1
	   03adf42c988195b50e1a1935ba5fcbc39b2b029b
	   ...

EXAMPLE
       To show all references called "master", whether tags or heads or anything else, and regardless of how deep in the reference naming
       hierarchy they are, use:

		   git show-ref master

       This will show "refs/heads/master" but also "refs/remote/other-repo/master", if such references exists.

       When using the --verify flag, the command requires an exact path:

		   git show-ref --verify refs/heads/master

       will only match the exact branch called "master".

       If nothing matches, git show-ref will return an error code of 1, and in the case of verification, it will show an error message.

       For scripting, you can ask it to be quiet with the "--quiet" flag, which allows you to do things like

		   git show-ref --quiet --verify -- "refs/heads/$headname" ||
			   echo "$headname is not a valid branch"

       to check whether a particular branch exists or not (notice how we don't actually want to show any results, and we want to use the full
       refname for it in order to not trigger the problem with ambiguous partial matches).

       To show only tags, or only proper branch heads, use "--tags" and/or "--heads" respectively (using both means that it shows tags and heads,
       but not other random references under the refs/ subdirectory).

       To do automatic tag object dereferencing, use the "-d" or "--dereference" flag, so you can do

		   git show-ref --tags --dereference

       to get a listing of all tags together with what they dereference.

FILES
       .git/refs/*, .git/packed-refs

SEE ALSO
       git-for-each-ref(1), git-ls-remote(1), git-update-ref(1), gitrepository-layout(5)

GIT
       Part of the git(1) suite

Git 2.17.1							    10/05/2018							   GIT-SHOW-REF(1)
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