Previously… Useful bash functions

This new version is a tad more efficient since there are no more echo and pipes involved on the processing. Just one eval and one awk script.


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unique_path() {
  eval $(awk -v VAR="${1}" 'BEGIN {                 \
    if((N=split(ENVIRON[VAR],vals,":"))<2) exit(0); \
    sep = out="" ; i=split(out,seen);               \
    do { if(!(vals[++i] in seen)) { seen[vals[i]];  \
           gsub("["]","\\"",vals[i]);             \
           out=sprintf("%s%s%s",out,sep,vals[i]);   \
           sep=":";                                 \
    } } while (i<N);                                \
    printf "%s="%s"; export %s;\n",VAR,out,VAR;   \
  }'
/dev/null)
}

Similarly, these also had remove unnecessary uses of sub-shell echo…


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safe_prepend_path() {
  VAR=$1 ; shift ; eval VAL=\$${VAR}
  for i_;do [ -d "$i_" ] && VAL=$i_${VAL:+":$VAL"} ;done
  eval export ${VAR}=${VAL}
}

safe_append_path() {
  VAR=$1 ; shift ; eval VAL=\$${VAR}
  for i_;do [ -d "$i_" ] && VAL=${VAL:+"$VAL:"}$i_ ;done
  eval export ${VAR}=${VAL}
}

If you, like me, strive to keep a well organized and modular configuration setup, sooner or later will split your bash configuration into multiple files. And if you want it to be valid for multiple machines you’ll appreciate the following function:


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source_if_exists () {
    for i_; do test -f "$i_" && source "$i_"; done
}

This way, you can try to process other configuration fragments only when they exist:


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source_if_exists ${HOME}/etc/bash_completion

Another common need for bash configuration is to either append or prepend paths to an environment variable. When doing a configuration for multiple machines it is always a pain to make sure those paths exist. These functions take care of that making adding directories to the path a breeze:


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safe_prepend_path() {
    VAR=$1
    shift
    VAL=$(eval echo \$${VAR})
    for i_; do
        test -d "$i_" && VAL=$i_${VAL:+":$VAL"}
    done
    eval export ${VAR}=$(echo ${VAL})
}

safe_append_path() {
    VAR=$1
    shift
    VAL=$(eval echo \$${VAR})
    for i_; do
        test -d "$i_" && VAL=${VAL:+"$VAL:"}$i_
    done
    eval export ${VAR}=$(echo ${VAL})
}

Example:


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safe_prepend_path PATH /opt/local/bin ${HOME}/bin
safe_append_path MANPATH /opt/local/man ${HOME}/man

Also, it is not unusual to have some path variables with duplicate entries, which is not very efficient. This function makes sure that a path only occurs once, and retains only the first occurrence, thus keeping the search order intact.


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unique_path() {
    eval export $1=$(echo $(eval echo \$${1}) | \
        awk -F:                   \
        '{ a[$1];                 \
           printf "%s",$1;        \
           for(i=2;i<=NF;i++) {   \
             if(!($i in a)) {     \
               printf ":%s",$i;   \
             };                   \
             a[$i];               \
           };                     \
           printf "\n";           \
         }'
)
}

Example:


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unique_path PATH
unique_path MANPATH
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