shell编程易错点总结.doc

QUOTE:1. for i in ls *.mp3for i in ls *.mp3; do? ?# Wrong!for.in 01 - Dont Eat the Yellow Snow.mp3 i 01-Dontls *.mp3for i in ls *.mp3; do? ?# Wrong!for i in *.mp3; do2. cp $file $target cp $file $target - cp cp - $file $target - for i in ./*.mp3; do?cp $i /target?.3. $foo = bar $foo = bar $foo multiple words here = bar $foo = bar ? ? ?# $foo - bash $foo = bar ? ? ?# bash x$foo = xbar ? ? # Java bar = $foo ? ? ?# 4. cd dirname $fcd dirname $fdirname Cbash $()cd $(dirname $f)5. $foo = bar & $bar = foo & test & bar = $foo -a foo = $bar ? ? ? # Right! bar = $foo & foo = $bar ? ?# Also right! $foo = bar & $bar = foo ? ? ? ?# Also right!6. $foo 7 ( $foo 7 ) $foo -gt 7 -gt $foo $foo -gt 7 7. grep foo bar | while read line; do (count+) ); done grep foo bar | while read line; do (count+); done? ? ? ?# barfoogrep -c foo bar grep foo bar | wc -lcountshellshell count8. if grep foo myfile if if test if Cif if then if grep foo myfile /dev/null; then9. if bar=$foo if if bar = $foo 10. if a = b & c = d if Cif a = b & c = d ? ? ?# 11. cat file | sed s/foo/bar/ file file0mv sed s/foo/bar/g file tmpfile & mv tmpfile file12. echo $fooMSG=Please enter a file name of the form *.zipecho $MSG? ? ? ?# zipPlease enter a file name of the form freenfss.zip lw35nfss.zipecho13. $foo=bar $ PerlPHP14. foo = barC15. echo EOFhere documenthere documentcatecho# This is wrong:echo EOFHello worldEOF# This is right:cat 7 ( $foo 7 ) $foo -gt 7 -gt $foo $foo -gt 7 7. grep foo bar | while read line; do (count+) ); done grep foo bar | while read line; do (count+); done? ? ? ?# barfoogrep -c foo bar grep foo bar | wc -lcountshellshell count8. if grep foo myfile if if test if Cif if then if grep foo myfile /dev/null; then9. if bar=$foo if if bar = $foo 10. if a = b & c = d if Cif a = b & c = d ? ? ?# 11. cat file | sed s/foo/bar/ file file0 mvsed s/foo/bar/g file tmpfile & mv tmpfile file12. echo $fooMSG=Please enter a file name of the form *.zipecho $MSG? ? ? ?# zipPlease enter a file name of the form freenfss.zip lw35nfss.zip echo13. $foo=bar $ PerlPHP14. foo = barC15. echo EOFhere documenthere documentcatecho# This is wrong:echo EOFHello worldEOF# This is right:cat EOFHello worldEOF16. su -c some command -c some command shell su -c su some command shellsu root -c some command man su -c - c, -commmand=COMMAND? ? ? ? ?pass a single COMMAND to the shell with -c -c some command -c some command shell17. cd /foo; barcd bar cdcd /foo & bar cd |cd /foo | exit 1;barbaz shellfind . -type d | while read subdir; do?cd $subdir & whatever & . & cd -done find . -type d | while read subdir; do?(cd $subdir & whatever & .)done shellshellshellshellcd - pushdpopddirs 18. bar = $foo = bar = $foo & echo yes bar = $foo & echo yes19. for i in 1.10; do ./something &; done& ; & ;for i in 1.10; do ./something & done20. cmd1 & cmd2 | cmd3 if.then.else cmd2cmd3 if cmd1; then cmd2; else cmd3 21. UTF-8BOM(Byte-Order Marks)UTF-8 BOMUnixUTF-8BOMBOMshell #!/bin/sh MS-DOS(CRLF)shell DOS$ ./dos-bash: ./dos: /bin/shM: bad interpreter: No such file or directory22. echo Hello World!- bash: !: event not found ! shell!$ echo hi!hi! $ echo Hello, world! set +H set +Hecho Hello, world!23. for arg in $*$*#!/bin/bash# Incorrect versionfor x in $*; do?echo parameter: $xdone$ ./myscript arg 1 arg2 arg3parameter: argparameter: 1parameter: arg2parameter: arg3 $#!/bin/bash# Correct versionfor x in $; do?echo parameter: $xdone$ ./myscript arg 1 arg2 arg3parameter: arg 1parameter: arg2parameter: arg3 bash $* $ *? ? Expands to the positional parameters, starting from one.? ? ? When the expansion occurs within double quotes, it? ? ?expands to a single word with the value of each parameter? ? ?separated by the first character of the IFS special variable.? ? ? That is, $* is equivalent to $1c$2c.,? ? Expands to the positional parameters, starting from