Utils

rltyty included in IT

2025-07-28 391 words

Contents

POSIX Shell

`?`

? is a pathname expansion (globbing) operator

?? matches any path name of length 2 in current directory

> echo ??
db
> echo ???
lib pty
> echo ????
ipc1 ipc2 proc
> echo ?????
advio intro stdio

awk

read a file line by line

#!/usr/bin/awk -f

BEGIN {
    while (getline < "test.awk.input" > 0) {
        printf("[%s] | [%s]\n", $1, $2);
    }
    close("test.awk.input")
    exit
}
END {
    printf("Argentina Vamos!\n")
}

This can be used to generate files. (See below Makefile, Ch.2 standards)

Makefile

Use implicit rules and awk to generate files.

Note: A implicit rule is followed by NO recipes!!!

conf:	conf.c

conf.c:	makeconf.awk sysconf.sym pathconf.sym
	$(AWK) -f makeconf.awk >conf.c

sysconf.sym:	sysconf-lim.sym
	grep -v "^#" sysconf-lim.sym >sysconf.sym

pathconf.sym:	pathconf-lim.sym
	grep -v "^#" pathconf-lim.sym >pathconf.sym

grep

Inverse match `-v`

Ex. Ignore all comments

grep -v "^#" in > out

Markdown

jump to header

An implicit id will be generated for a header during markdown-to-html process by replacing internal spaces with hyphens and making lowercase.

## The Header

[Jump to the header](#the-header)

This is equivalent to

<a href="#the-header">Link Text</a>

od - octal, decimal, hex, ASCII dump

-c, C-style escaped characters, -h, hexadecimal shorts, -a ASCII named chars.

od -c file.hole

0000000    a   b   c   d   e   f   g   h   i   j  \0  \0  \0  \0  \0  \0
0000020   \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0040000    A   B   C   D   E   F   G   H   I   J
0040012

od -h ./file.hole
0000000      6261    6463    6665    6867    6a69    0000    0000    0000
0000020      0000    0000    0000    0000    0000    0000    0000    0000
*
0040000      4241    4443    4645    4847    4a49
0040012

od -a ./file.hole
0000000    a   b   c   d   e   f   g   h   i   j nul nul nul nul nul nul
0000020  nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
*
0040000    A   B   C   D   E   F   G   H   I   J
0040012

NOTE

offset in octal
In octal, 6261 -> 9897 -> ab, 4241 -> 6665 -> AB

getconf(1)

Retrieve standard configuration variables

 getconf -a [file]
 getconf [-v environment] path_var file
 getconf [-v environment] system_var

E.g.

getconf NAME_MAX ./aaa
255
getconf PATH_MAX ./aaa
1024
getconf -v POSIX_V6_LP64_OFF64 UINT_MAX
4294967295
getconf -v POSIX_V6_LP64_OFF64 INT_MAX
2147483647
getconf -v POSIX_V6_LP64_OFF64 FILESIZEBITS ./aaa
56

Zathura

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