Bash Index : X - Httqm's Docs

xz-utils

Compress or decompress .xz and .lzma files

Flag	Usage
-d --decompress --uncompress	(explicit) alternate : unxz myFile.xz

compress a file: xz path/to/file
decompress a file: xz --decompress path/to/file.xz

make a hex dump or do the reverse

this can be used to convert ASCII characters into their hexadecimal code

So far, I'm only considering this tool in the context of URL encoding/decoding.

Flag	Usage
-p -plain	output result in PostScript continuous hex dump style aka plain
-r -revert	convert hex dump into binary

convert ASCII characters into their hexadecimal code :

For reference, we'll play with the H character, which has the 48 hexadecimal value in the ASCII table

echo -n 'H' | xxd -p
48

echo -n '\x48' | xxd -r -p
H

Same thing with [BACKSPACE] aka \x08 :

echo -n 'ABC'; echo -n '\x08' | xxd -r -p
AB

When receiving results piped from find, xargs outputs the error :

find | xargs

xargs: unmatched single quote; by default quotes are special to xargs unless you use the -0 option

When I got this error, some of the returned files actually had single quotes ' in their path / name / both (not checked whether the number of quotes was even or not in the path / name / both : xargs seemed unhappy anyway).

Trying the -0 option alone as "suggested" by the error message won't fix anything : it will turn the n find results (file names) into a unique giant result which is the concatenation of all the file names (read more in the solution below).

Workaround

Instead of using a construct such as :

find | xargs

consider a while read with process substitution construct :

while read fileName; do
	# do something
done < <(find )

Solution

You may use xargs' -0 option provided find feeds it correctly :

find -print0 | xargs -0

Construct argument lists and invoke utility : xargs options utility

xargs may return exit codes such as 123, 124, 125, 126 or 127 if something went wrong when calling 'utility' (for details : ).

Different kinds of lists :

"chained" lists, aka whitespace-separated lists :
echo 'a b c'
```
a b c
```
"stacked" lists, aka newline-separated lists :
echo -e 'a\nb\nc'
```
a
b
c
```

There is no such distinction between list types, but I use these to make examples below easier to explain.

By default, xargs reads stacked lists.

Flag	Usage
-0 --null	input items are terminated by a `null` character instead of by whitespace quotes and backslash are not special (every character is taken literally) disables the end of file string, which is treated like any other argument Useful when input items might contain white space, quote marks, or backslashes. The GNU find -print0 option produces input suitable for this mode.
-I pattern ~~-i pattern~~ ~~--replace=pattern~~	replace pattern with values piped into xargs (example) implies -x and -L 1 : i.e. : pop 1 item out of a stacked list doesn't work with chained lists -i and --replace are deprecated
-L n --max-lines=n ~~-l n~~	use at most n nonblank input lines per command line trailing blanks cause an input line to be logically continued on the next input line implies -x examples : -L n, -L 1 -L n : n must be specified --max-lines=n : n defaults to 1 -l : deprecated
-n n	Pop n arguments at a time from the list to feed utility
-P n	Execute at most n parallel instances of utility. Defaults to 1. (source). -n should be specified when using -P or there is a risk of firing only 1 instance of utility.
-s maxChars --max-chars=maxChars	use at most maxChars characters per command line default value is system-dependant, no idea how to get it exactly
-x	exit if the size specified with -s is exceeded

Using -L :

echo -e {a..z}"\n" | xargs -L 12 echo

a b c d e f g h i j k l
m n o p q r s t u v w x
y z

echo -e 'a\nb\nc\nd\ne' | xargs -L 2 echo

a b
c d
e

echo -e 'a\nb \nc\nd\ne' | xargs -L 2 echo

a b c
d e

Using -L 1 :

echo -e 'a\nb\nc' | xargs -L 1 echo

a
b
c

echo -e 'a\nb\nc' | xargs -I foo echo foo

a
b
c

echo 'a b c' | xargs -L 1 echo

a b c

echo 'a b c' | xargs -I foo echo foo

a b c

tar all files of the current directory :

find -maxdepth 1 -type f | xargs tar cf archive.tar

Download all URLs listed in a file (source) :

cat urlList.txt | xargs wget -c

This example, albeit quite functional, is actually deprecated by wget's -i.

Archive the n latest files matching pattern :

ls -t *pattern* | head -n n | xargs tar cfz /path/to/archive.tgz

Cannot umount a filesystem because of open files ? Kill, kill, KILL !!! :

Killing so many processes this way is VERY! BAD!. Do this only if :

these processes are started at boot time
AND you can not switch to a lower runlevel
AND you can not stop them all
AND you plan to reboot shortly
AND (many other reasons to convince you this is a bad thing )

lsof /mnt/myFilesystem | awk '{print $2}' | sed '1d' | xargs kill -15

How to use the values piped to xargs into its sub-command ?

for i in {1..5}; do echo $i; done | xargs -I pattern echo 'this is line pattern.'

It's like xargs substitutions have precedence over Bash.

Use values more than once :

for i in {a..e}; do echo $i; done | xargs -I whatIWant sh -c 'echo -n "I can say \"whatIWant\"."; echo " And I can say it even louder : \"$(echo whatIWant | tr '[:lower:]' '[:upper:]') !\""'

sh -c 'someCommand' above means run someCommand within the /bin/sh shell. Some advanced commands / flags / options may not be available in this shell. Consider bash -c 'someCommand' then.

Call a function within the same script

#!/usr/bin/env bash

myStackedList=$(echo {a..z} | tr ' ' '\n')	just generating a stacked list
echo "$myStackedList" | xargs -L 12 echo	and displaying it as slices of 12 grouped letters
echo

doSomething() {		a dummy function that "does things", needed for the demo
	echo "$@,"
	}

export -f doSomething	this makes the exported function exist as a command available to xargs (source)
echo "$myStackedList" | xargs -L 12 bash -c 'doSomething "$@"' _read details below

a b c d e f g h i j k l
m n o p q r s t u v w x
y z

a b c d e f g h i j k l,
m n o p q r s t u v w x,
y z,

the `bash -c 'doSomething "$@"' _` part :

bash -c 'command' : run command within Bash
doSomething "$@" : this passes along all arguments provided to command to the doSomething function
the trailing _ :
- serves as a placeholder for $0 (i.e. shell name), to be used in warning and error messages
- many different characters may be used, I don't know where this usage comes from
- full details : man -P 'less -p "-c option"' bash (mankier.com, gnu.org)

Bash Index : X - The 'X' Bash commands : description, flags and examples

xz

Installed with the Debian package

Usage

Flags

Example

xxd

Usage

Flags

Example

convert ASCII characters into their hexadecimal code :

xargs: unmatched single quote; by default quotes are special to xargs unless you use the -0 option

Workaround

Solution

xargs

Usage

Different kinds of lists :

Flags

Example

Using -L :

Using -L 1 :

tar all files of the current directory :

Download all URLs listed in a file (source) :

Archive the n latest files matching pattern :

Cannot umount a filesystem because of open files ? Kill, kill, KILL !!! :

How to use the values piped to xargs into its sub-command ?

Use values more than once :

Call a function within the same script

the `bash -c 'doSomething "$@"' _` part :

xz

Installed with the Debian package

Usage

Flags

Example

xxd

Usage

Flags

Example

convert ASCII characters into their hexadecimal code :

xargs: unmatched single quote; by default quotes are special to xargs unless you use the -0 option

Workaround

Solution

xargs

Usage

Different kinds of lists :

Flags

Example

Using -L :

Using -L 1 :

tar all files of the current directory :

Download all URLs listed in a file (source) :

Archive the n latest files matching pattern :

Cannot umount a filesystem because of open files ? Kill, kill, KILL !!! :

How to use the values piped to xargs into its sub-command ?

Use values more than once :

Call a function within the same script

the bash -c 'doSomething "$@"' _ part :

the `bash -c 'doSomething "$@"' _` part :