September 13, 2015 Course assignments-Questions about the shell

1. Describe the operation principle of shell program (can be attached with necessary graphic instructions);

s after system kernel execution.

2, summarize all the knowledge points involved in shell programming (such as: variables, grammar, command status, etc., to take the picture of Yo);

The following instance is from Iredmail's installation script tmprootdir= "$ (dirname $0)"   //defines the temp directory, which is the variable in the shell Echo ${tmprootdir}  | grep  ' ^/'  >/dev/null 2>&1if [ x "$?"  == x "0"  ]; then   //determine whether to perform     export based on the last command state above  rootdir= "${tmprootdir}"   //uses both the command state and the If Judgment else    export rootdir= "$ ( PWD) "fi# create ssl/tls cert file.check_status_before_run generate_ssl_keys   //check_status_before_run is a function # The following is the definition of this function check_status_before_run () {    # if  function was successfully executed, this function will write one  line    # in  $STATUS _file:    #     #   export status_[function_name]= ' Done '     #     function_name= "${1}"   //use positional parameters to get variable values  &NBSp;  function_status_name= "Status_${function_name}"     function_status_value= "$ ( Eval echo \$${function_status_name}) "    if [ x" ${function_status_ Value} " == x" Done " ]; then        ECHO_SKIP " Function: $1. "     else         $function _name          #if  [ x "$?"  == x ' 0 '  ]; then        #     echo  "export ${function_status_name}= ' Done '"  >> ${STATUS_FILE}          #fi     fi} #另一个函数的定义 with a For loop, if Judgment Backup_file () {     # Usage: backup_file file1 [file2 file3 ... fileN]     if [ x "$#"  != x "0"  ]; then   //$#  the number of arguments added to the shell         for conf_ file in [email protected]; do  //using a For loop to read the configuration file,             if [ -f ${conf_file} ]; then                 if [ x "${ Iredmail_debug} " == x" Yes " ]; then                     echo -e  "${_backup_flag} ${ conf_file} -> $ (Basename ${conf_file}). ${date}. "                 fi                 cp -f ${conf_ File} ${conf_file}.${date}            else                 :            fi         done    else         :    FI}

3, summarize the course of all the circular statement, the use of conditional judgment and related examples; (if (jpg|png is not exist); echo "You say a XX")

September 13, 2015 Course assignments-Questions about the shell