Shell Learning 45 days----Xargs

Execute command : Xargs

When find produces a list of files , It is sometimes useful to provide the list to another command .

Case :

$touch abc.c ERD.C oiy.c

$ll

./erd.c

./abc.c

./oiy.c

$find-name ' *.c ' | Rm

RM: missing operand

Please try "rm--help" for more information.

$find-name ' *.c ' | Xargs RM

$find-name ' *.c '

Without any display , the description was successfully deleted .

1. Introduction , the key to this command is that many commands do not support pipelines (|) to pass parameters , and it's necessary in daily work. , so there it is. Xargs Command , Above Example .

Xargs can read into the stdin data , and with a blank or a break in the cell as a resolution , will stdin data is separated into atguments because it is separated by a blank element , so , If there are some filenames or other meaningful nouns that contain white space , the Xargs may appear to be mistaken .

$touch ' file 1.log ' file 2.log '

$ll

Total dosage 0

-rw-r--r--1 root root 0 7 months 10:18 file 1.log

-rw-r--r--1 root root 0 7 months 10:18 file 2.log

$find-name ' *.log '

./file 2.log

./file 1.log

$find-name ' *.log ' | Xargs RM

RM: Cannot delete "./file": no file or directory

RM: Unable to delete "2.log": no file or directory

RM: Cannot delete "./file": no file or directory

RM: Unable to delete "1.log": no file or directory

The reason is simple , Xargs the default is to split the record with whitespace characters ( spaces , tabs, line breaks ) , so the file name ./file 1.log was interpreted as two records. ./file and the 1.log, Unfortunately, RM I can't find these two files . .

To solve this kind of problem,Smart man came up with a way,LetFindafter printing out a file name, then output aNULLcharacter(‘ ’)Instead of a newline character.,and then I'll tellXargsalso useNULLcharacter as the delimiter for the record,this isFindof the-printand theXargsof the-0Options.

$find-name ' *.log '-print0 | xargs-0 RM

2. Main options

Options	Meaning
-0	When stdin contains special sub-elements , It is treated as a general character
-A file	Read in file as stdin
-E Flag	Note that sometimes it may be -e,flag must be a space-delimited flag , when xargs is analyzed to contain flag Stop when this sign is on.
-P	Ask the user once every time a argument is executed .
-N num	The number of times added , indicating that the command executes at the time of the arguments number , By default is used all .
-T	is to print the command first and then execute the
-I.	Or- I, the name of each item in the xargs , usually a row of the assignment to {}, you can use {} instead of
-R No-run-if-enpty	When the input of the Xargs is empty, it stops Xargs and does not need to be executed again.
-S NUM	Maximum number of characters on the command line
-D Delim	Delimiter , the default xargs delimiter is carriage return , argument delimiter is a space , here is modified delimiter for Xargs
-X	Exit means that the main match - s is used
-P	Modify the maximum number of processes, default is 1, 0 when as Mang as it can

the difference between find-print and -print0 :

-print a carriage return newline character is added after each output , and -print0 does not .

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Shell Learning 45 days----Xargs