Pull values in a variable from another variable

Question

I am trying to pull a value from a sequence, based on the entry of the parameter in the file. In my case, the values are going to be either "seq", "date", or "count".

function ParseHeader {
    local varHeaderLine=$1
    local varType=$2
    local varOut=""
    
    if [[ -z "$varType" ]]; then
        echo "Cannot find! - ($varType)"
        exit 1
        
    elif [[ "$varType" = "seq" ]]; then
        varOut=$(echo "$varHeaderLine" | cut -d\| -f 3)
        echo "Sequence: $varOut"
    elif [[ "$varType" = "date" ]]; then
        varOut=$(echo "$varHeaderLine" | cut -d\| -f 4)
        echo "Date: $varOut"
    elif [[ "$varType" = "count" ]]; then
        varOut=$(echo "$varHeaderLine" | cut -d\| -f 5)
        echo "Line Count: $varOut"
    else
        echo "Invalid input! Your Header is: $varHeaderLine"
    fi
        return $?
}

sequence='XXXXX|Y|1|20220429|9999'

ProfSeq=$(ParseHeader "${sequence}" "count")


echo $ProfSeq

This is a piece out of the whole file, but what is happening here is that I am going to receive a file, pull its sequence, and then pull some value from that particular sequence. Thanks for the help, this is what I ended up with. Now I'm looking for it to be less CPU intensive, if possible.

Note: This piece is out of a while file script that will be running daily for different servers in different environments

Answer 1

Focusing solely on the current piece of code ...

Assumptions/Understandings:

• the variable ProfSeq is to contain the output from the function's echo calls; we can eliminate the subprocess call (ProfSeq=$( ... subprocess call ...)) by having the function replace the echo "..." calls with ProfSeq="..." (ie, have the function directly populate the ProfSeq variable
• additional performance improvements can be derived from eliminating the double subprocess calls to split varHeaderLine ($(echo ... | cut ...)) with the bash/read builtin

One idea for a function rewrite:

ParseCOTHeader () {

local varHeaderLine=$1
local -l varType=$2                                # force to all lowercase
local ignore1 ignore2 in_seq in_date in_count rc

# split varHeaderLine into 5 variables based on '|' delimiter:
# NOTE: assumes varHeaderLine has exactly 5x '|' delimited fields otherwise OP
#       may want to add some code to validate the structure of varHeaderLine

IFS='|' read -r ignore1 ignore2 in_seq in_date in_count <<< "${varHeaderLine}"

# reset variables:

ProfSeq=
rc=0

if [[ -z "${varType}" ]]
then
    ProfSeq="Cannot find! - ($2)"                  # since varType=$2 is empty at this point we will always print '()' ... ?
    rc=1
else
    case "${varType}" in
         seq)    ProfSeq="Sequence: ${in_seq}" ;;
         date)   ProfSeq="Date: ${in_date}" ;;
         count)  ProfSeq="Line Count: ${in_count}" ;;
         *)      ProfSeq="Invalid input! Your Header is: '$varHeaderLine'"
                 rc=1 ;;
    esac
fi

return "${rc}"
}

Putting the function through its paces:

$ sequence='SWHHR|H|1|20220429|9999'

$ ParseCOTHeader "${sequence}" 'seq'
$ echo "$? : ${ProfSeq}"
0 : Sequence: 1

$ ParseCOTHeader "${sequence}" 'DaTe'
$ echo "$? : ${ProfSeq}"
0 : Date: 20220429

$ ParseCOTHeader "${sequence}" 'COUNT'
$ echo "$? : ${ProfSeq}"
0 : Line Count: 9999

$ ParseCOTHeader "${sequence}" 'fire-truck'
$ echo "$? : ${ProfSeq}"
1 : Invalid input! Your Header is: 'SWHHR|H|1|20220429|9999'

$ ParseCOTHeader "${sequence}" ''
$ echo "$? : ${ProfSeq}"
1 : Cannot find! - ()

---

If repeated calls to the function need to save the message string in different variables:

• add the line local -n myoutput=$3 in the top section of the function (this defines a local nameref variable myoutput to act as a pointer to the variable name passed in $3)
• replace all ProfSeq="..." with myoutput="..." in the function
• remove the line ProfSeq= (variable reset) in the function

Taking the new function for a test spin:

$ sequence='SWHHR|H|1|20220429|9999'

$ ParseCOTHeader "${sequence}" 'seq' ProfSeq
$ echo "$? : ${ProfSeq}"
0 : Sequence: 1

$ ParseCOTHeader "${sequence}" 'DaTe' ProfSeq
$ echo "$? : ${ProfSeq}"
0 : Date: 20220429

$ ParseCOTHeader "${sequence}" 'COUNT' ProfSeq
$ echo "$? : ${ProfSeq}"
0 : Line Count: 9999

$ ParseCOTHeader "${sequence}" 'fire-truck' SomeOtherVar
$ echo "$? : ${SomeOtherVar}"
1 : Invalid input! Your Header is: 'SWHHR|H|1|20220429|9999'

$ ParseCOTHeader "${sequence}" '' YetAnotherVar
$ echo "$? : ${YetAnotherVar}"
1 : Cannot find! - ()