davidsen@steinmetz.UUCP (William E. Davidsen Jr) (11/18/87)
Some years ago I wrote this to allow a portable of extracting substrings
from expressions other than by use of awk. I finally got around to
writing a man page for it, and I hope it's useful.
:
#!/bin/sh
# shar+ created from directory /usr2/davidsen/doc
# 15:46 on Mon Nov 16, 1987 by davidsen
echo 'x - substr.1 (text)'
sed << 'E!O!F' 's/^X//' > substr.1
X'\" @(#)Documentation for the 'substr' command
X'\" * * * this man page requires the 'tbl' preprocessor * * *
X.TH substr 1
X.SH NAME
Xsubstr - extract a substring from the input arguments
X.SH SYNOPSIS
Xsubstr string start_char num_of_char
X.SH DESCRIPTION
Xsubstr extracts characters from a string provided as the first argument, and
Xwrites the characters extracted to standard output. This avoids having
Xto use other proprietary methods to accomplish extraction.
X.SS Special values
XThe second argument is the first character to be extracted. Numbering is
Xfrom one rather than zero. If the starting value is negative it is
Xrelative to the last character, such as -2 means the last two characters
Xin the first argument.
XThe third argument is the number of characters to extract.
XIf the third argument is zero, all characters right of the starting
Xposition are extracted. If the length
Xargument is negative, it is adjusted to end relative to the end of the
Xstring. A value of -2 would end the extraction trimming the last two
Xcharacters from the string.
X.SH EXAMPLES
XTo force an update of all SCCS files open for editing in the current
Xdirectory, and display a list of changes to the user.
X.in +.5i
X.nf
Xfor pname in p.*
Xdo
X name=`substr $pname 3 0`
X get -p -k s.$name | diff - $name
X delta s.$name
Xdone
X.fi
X.in -.5i
X.SS Table of examples
X.TS
Xbox;
Xl c c l, l n n l.
Xstart 1st col width extracted
Xstring argument argument characters
X_
X123456 1 4 1234
X123456 3 2 34
X123456 2 0 23456
X123456 2 -2 234
X123456 -3 1 4
X123456 -4 0 3456
X.TE
X.SH WARNINGS
XNo error messages are produced, but the status returned is non-zero if
Xthe operation fails. Having the length requested greater than the
Xcharacters available is not an error.
X.SH LIMITATION
XThe usage of negative numbers for the starting character and length
Xis not consistant. This was done so that "-2" for a start could mean use
Xthe last two characters, and "-2" for a length would strip the last two
Xcharacters.
X.SH AUTHOR
XBill Davidsen, GE Corporate R&D Center, davidsen@crdos1.uucp
X'\" For more details, see man(7), as well as man(1), manroff(1), and mmt(1)
E!O!F
newsize=`wc -c < substr.1`
if [ $newsize -ne 2100 ]
then echo "File substr.1 was $newsize bytes, 2100 expected"
fi
echo 'x - substr.c (text)'
sed << 'E!O!F' 's/^X//' > substr.c
X#include <stdio.h>
X
Xstatic char SCCSid[] = {"@(#)substr.c v1.2 - 11/16/87"};
X
Xmain (argc, argv)
X int argc;
X char *argv[];
X{
X register char *ptr;
X register char ch;
X int start, end; /* first and last character to extract */
X int slen; /* string length */
X
X if (argc < 4)
X exit (0);
X start = atoi (argv[2]);
X end = atoi (argv[3]);
X slen = strlen(argv[1]);
X if (slen == 0) exit(1);
X
X /* test for special values */
X if (start < 0)
X start += slen + 1;
X if (end == 0)
X end = slen - start + 1;
X else if (end < 0)
X end += slen - (start - 1);
X
X /* validate the values */
X if (start < 1 || end < 1)
X exit (1);
X
X ptr = argv[1] + start - 1;
X while (end-- && (ch = *ptr++))
X putchar (ch);
X putchar ('\n');
X exit(0);
X}
E!O!F
newsize=`wc -c < substr.c`
if [ $newsize -ne 791 ]
then echo "File substr.c was $newsize bytes, 791 expected"
fi
exit 0
--
bill davidsen (wedu@ge-crd.arpa)
{uunet | philabs | seismo}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me