Mostrando mensaje 1165     < Anterior | Siguiente > Responder a este mensaje Asunto: [glisc] Introducción a BASH shell scripting Fecha: Miercoles, 2 de Abril, 2003  16:32:13 (-0400) Autor: Alfonso Fernandez <afernandez @........bo> Introduction to Shell Scripting http://www.linuxgazette.com/issue53/okopnik.html "FOR;DO;DONE" Often, scripts are written to automate some repetitive task; as a random example, if you have to repeatedly edit a series of files in a specific directory, you might have a script that looks like this: --------------------------------------------------------------------------- - #!/bin/bash for n in ~/weekly/*.txt do ae $n done echo "Done." --------------------------------------------------------------------------- - #!/bin/bash for n in ~/weekly/*.txt; do ae $n; done; echo "Done." "WHILE;DO;DONE" Often, we need a control mechanism that acts based on a specified condition rather than iterating through a list. The 'while' loop fills this requirement: --------------------------------------------------------------------------- ----- #!/bin/bash pppd call provider & while [ -n "$(ping -c 1 192.168.0.1|grep 100%)" ] do echo "Connecting..." done echo "Connection established." "UNTIL;DO;DONE" The 'until' loop is the reverse of the 'while' - it continues to loop as long as the test is false, and fails when it becomes true. I've never had the occasion to use it; the 'while' loop and the flexibility of the available tests have sufficed for everything I've needed so far. "IF;THEN;[ELSE];FI" There are many times when we just need to check for the existence of a condition and branch the execution based on the result. For those times, we have the 'if' statement: --------------------------------------------------------------------------- ---- ... if [ $BOSS="jerk" ] then echo 'Take this job and shove it!' else echo 'Stick around; the money is good.' fi ... "CASE;IN;;ESAC" The remaining tool that we can use for conditional branching is basically a multiple 'if' statement, based on the evaluation of a test. If, for example, we know that the only possible outputs from an imaginary program called 'intel_cpu_test' are 4, 8, 16, 32, or 64, then we can write the following: --------------------------------------------------------------------------- ----- #!/bin/bash case $(intel_cpu_test) in 4) echo "You're running Linux on a calculator??";; 8) echo "That 8088 is past retirement age...";; 16) echo "A 286 kinda guy, are you?";; 32) echo "One of them new-fangled gadgets!";; 64) echo "Oooh... serious CPU envy!";; *) echo "What the heck are you running, anyway?";; esac BREAK and CONTINUE These statements interrupt the program flow in specific ways. The "break", once executed, immediately exits the enclosing loop; the "continue" statement skips the current loop iteration. This is useful in a number of situations, particularly in long loops where the existence of a given condition makes all further tests unnecessary. DATE EXAMPLE --------------------------------------------------------------------------- ----- #!/bin/bash # "bkup" - copies specified files to the user's ~/Backup # directory after checking for name conflicts. a=$(date +%T-%d_%m_%Y) cp -i $1 ~/Backup/$1.$a _______________________________________________________________________ ~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~ !!Tu correo gratuito para siempre!! 10 megabytes de espacio, agenda de direcciones, filtro anti-spam, etc. garantizado de funcionar siempre con eListas.net y por supuesto con el resto de Internet... Y si lo deseas, obten igualmente revistas gratis en tu casa, acceso libre a webs exclusivas, descargas, libros electrónicos... y sorteos trimestrales de 1.000 euros. !!En GeoMundos!! Haz clic aquí ¡YA! -> http://elistas.net/ml/119/ ~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~