xargs(C) 19 June 1992 xargs(C) Name xargs - construct and execute commands Syntax xargs [ flags ] [ command [ initial-arguments ] ] Description The xargs command combines the fixed initial-arguments with arguments read from the standard input to execute the specified command one or more times. The number of arguments read for each command invocation and the manner in which they are combined are determined by the flags specified. command, which may be a shell file, is searched for using the shell $PATH variable. If command is omitted, /bin/echo is used. Arguments read in from standard input are defined to be contiguous strings of characters delimited by one or more blanks, tabs, or newlines; empty lines are always discarded. Blanks and tabs may be embedded as part of an argument if escaped or quoted: Characters enclosed in quotes (single or double) are taken literally, and the delimiting quotes are removed. Outside of quoted strings, a backslash (\) will escape the next character. Each argument list is constructed starting with the initial-arguments, followed by some number of arguments read from standard input (exception: see -i flag). Flags -i, -l, and -n determine how arguments are selected for each command invocation. When none of these flags are coded, the initial-arguments are followed by arguments read continuously from stan- dard input until an internal buffer is full, and command is executed with the accumulated args. This process is repeated until there are no more args. When there are flag conflicts (for example, -l vs. -n), the last flag has precedence. flag values are: -lnumber command is executed for each number lines of nonempty argu- ments from the standard input. This is instead of the default single line of input for each command. The last invo- cation of command will be with fewer lines of arguments if fewer than number remain. A line is considered to end with the first newline unless the last character of the line is a blank or a tab; a trailing blank/tab signals continuation through the next nonempty line. If number is omitted, 1 is assumed. Option -x is forced. -ireplstr Insert mode: command is executed for each line from the stan- dard input, taking the entire line as a single argument, inserting it in initial-arguments for each occurrence of replstr. A maximum of 5 arguments in initial-arguments may each contain one or more instances of replstr. Blanks and tabs at the beginning of each line are thrown away. Con- structed arguments may not grow larger than 255 characters, and option -x is also forced. ``{ }'' is assumed for replstr if not specified. -nnumber Executes command, using as many standard input arguments as possible, up to the number of arguments maximum. Fewer argu- ments are used if their total size is greater than size char- acters, and for the last invocation if there are fewer than number arguments remaining. If option -x is also coded, each number of arguments must fit in the size limitation, or xargs terminates execution. -t Trace mode: the command and each constructed argument list are echoed to file descriptor 2 just prior to their execu- tion. -p Prompt mode: the user is prompted whether to execute command at each invocation. Trace mode (-t) is turned on to display the command instance to be executed, followed by a ``?...'' prompt. A reply of ``y'' (optionally followed by anything), will execute the command; anything else, including a carriage return, skips that particular invocation of command. -x Causes xargs to terminate if any argument list would be greater than size characters; -x is forced by the options -i and -l. When none of the options -i, -l, or -n are coded, the total length of all arguments must be within the size limit. -ssize The maximum total size of each argument list is set to size characters; size must be a positive integer less than or equal to 470. If -s is not coded, 470 is taken as the default. Note that the character count for size includes one extra character for each argument and the count of characters in the command name. -eeofstr eofstr is taken as the logical end-of-file string. Under- score (_) is assumed for the logical EOF string if -e is not coded. -e with no eofstr coded turns off the logical EOF string capability (underscore is taken literally). xargs reads standard input until either end-of-file or the logical EOF string is encountered. xargs terminates if it either receives a return code of -1 from, or if it cannot execute, command. When command is a shell program, it should ex- plicitly exit (see sh(C)) with an appropriate value to avoid accidentally returning with -1. Examples The following will move all files from directory $1 to directory $2, and echo each move command just before doing it: ls $1 | xargs -i -t mv $1/{ } $2/{ } The following will combine the output of the parenthesized commands onto one line, which is then echoed to the end-of-file log: (logname; date; echo $0 $*) | xargs >>log The user is prompted to enter which files in the current directory are to be printed and prints them one at a time: ls | xargs -p -l lpr or many at a time: ls | xargs -p -l | xargs lpr The following will execute diff(C) with successive pairs of arguments originally entered as shell arguments: echo $* | xargs -n2 diff Standards conformance xargs is conformant with: AT&T SVID Issue 2; and X/Open Portability Guide, Issue 3, 1989.