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Top Forums UNIX for Beginners Questions & Answers Substitute a character with sed Post 303032286 by MadeInGermany on Thursday 14th of March 2019 06:10:18 PM
Old 03-14-2019
Bakunin's replacement code in post#4 is portable but still creates a new inode for the input file ("/path/to/file")
This not only denotes a repair of the original owner/group/permissions, it will make a previously hard-linked file stand-alone, and this damage cannot be repaired.
Also GNU sed -i (and perl -i) cannot preserve the original linkage.
If we are going for a real improvement then we avoid the mv command!
Code:
if sed '....' /path/to/file > /path/to/file.tmp ; then
     cp  /path/to/file.tmp  /path/to/file
else
     <error handling procedure here>
fi

The cp command preserves the original inode (owner/group/permissions and linkage) - only the timestamp changes, and that's pretty correct.
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STRMODE(3)                                                 BSD Library Functions Manual                                                 STRMODE(3)

NAME
strmode -- convert inode status information into a symbolic string LIBRARY
Utility functions from BSD systems (libbsd, -lbsd) SYNOPSIS
#include <bsd/string.h> void strmode(mode_t mode, char *bp); DESCRIPTION
The strmode() function converts a file mode (the type and permission information associated with an inode, see stat(2)) into a symbolic string which is stored in the location referenced by bp. This stored string is eleven characters in length plus a trailing NUL. The first character is the inode type, and will be one of the following: - regular file b block special c character special d directory l symbolic link p fifo s socket w whiteout ? unknown inode type The next nine characters encode three sets of permissions, in three characters each. The first three characters are the permissions for the owner of the file, the second three for the group the file belongs to, and the third for the ``other'', or default, set of users. Permission checking is done as specifically as possible. If read permission is denied to the owner of a file in the first set of permis- sions, the owner of the file will not be able to read the file. This is true even if the owner is in the file's group and the group permis- sions allow reading or the ``other'' permissions allow reading. If the first character of the three character set is an ``r'', the file is readable for that set of users; if a dash ``-'', it is not read- able. If the second character of the three character set is a ``w'', the file is writable for that set of users; if a dash ``-'', it is not writable. The third character is the first of the following characters that apply: S If the character is part of the owner permissions and the file is not executable or the directory is not searchable by the owner, and the set-user-id bit is set. S If the character is part of the group permissions and the file is not executable or the directory is not searchable by the group, and the set-group-id bit is set. T If the character is part of the other permissions and the file is not executable or the directory is not searchable by others, and the ``sticky'' (S_ISVTX) bit is set. s If the character is part of the owner permissions and the file is executable or the directory searchable by the owner, and the set- user-id bit is set. s If the character is part of the group permissions and the file is executable or the directory searchable by the group, and the set- group-id bit is set. t If the character is part of the other permissions and the file is executable or the directory searchable by others, and the ``sticky'' (S_ISVTX) bit is set. x The file is executable or the directory is searchable. - None of the above apply. The last character is a plus sign ``+'' if any there are any alternate or additional access control methods associated with the inode, other- wise it will be a space. SEE ALSO
chmod(1), find(1), stat(2), getmode(3), setmode(3) HISTORY
The strmode() function first appeared in 4.4BSD. BSD July 28, 1994 BSD
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