Shell – use printf to format output of an array

arrayprintfshell-script

I have an array that contains details about each NIC.
Each array index consists of three space-separated values.

I would like to have a nice table as output. Is there a way to assign formatting patterns to each value in an index?

so far this is what I use:

NIC_details[0]='wlp2s0 192.168.1.221 xx:xx:xx:xx:xx:xx'
NIC_details[1]='wwan0 none xx:xx:xx:xx:xx:xx'
NIC_details[2]='virbr0 192.168.122.1 00:00:00:00:00:00'

printf "%-20s\n" "${NIC_details[@]}"

Is there a way to access the values in an array index by their position $1, $2, and $3, knowing that they are space-separated, and then apply a formatting pattern for each $X position?

I have also tried

echo "$i" | column -t

but it does not bring the desired result.

Best Answer

Here's a slight modification to what you were already doing:

set -f # to prevent filename expansion
for i in ${!NIC_index[@]}
do
  printf "%-20s" ${NIC_details[i]}
  printf "\n"
done

I added a for loop to go over all of the array indexes -- that's the ${!NIC... syntax. Since it's a numeric array, you could alternatively loop directly over the indexes.

Note that I intentionally left ${NIC_details[i]} unquoted so that the shell would split the value on the spaces that you've used to separate the values. printf thus sees the 3 values and so repeats the %-20s formatting for each of them. I then add a newline after each NIC to make a nice table.

The set -f at the top is important if we leave variables unquoted; otherwise the shell will step in and attempt to glob any wildcards it sees in unquoted variables.

Sample output:

wlp2s0              192.168.1.221       xx:xx:xx:xx:xx:xx
wwan0               none                xx:xx:xx:xx:xx:xx
virbr0              192.168.122.1       00:00:00:00:00:00

Related Solutions

Bash Arrays – Using Variables in Array Names

Some ideas:

A "parameter expansion" of a variable value (the ${...} part):
```
echo "arr$COUNTER[0] = ${arr$COUNTER[0]}"
```
will not work. You may get around by using eval (but I do not recommend it):
```
eval echo "arr$COUNTER[0] = \${arr$COUNTER[0]}"
```
That line could be written as this:
```
i="arr$COUNTER[0]"; echo "$i = ${!i}"
```
That is called indirection (the !) in Bash.
A similar issue happens with this line:
```
declare -a "arr$COUNTER=($field)"
```
Which should be split into two lines, and eval used:
```
declare -a "arr$COUNTER"
eval arr$COUNTER\=$ \$field $
```
Again, I do not recommend using eval (in this case).
As you are reading the whole file into the memory of the shell, we may as well use a simpler method to get all lines into an array:
```
readarray -t lines <"VALUES_FILE.txt"
```
That should be faster than calling awk for each line.

An script with all the above could be:

#!/bin/bash
valfile="VALUES_FILE.txt"

readarray -t lines <"$valfile"             ### read all lines in.

line_count="${#lines[@]}"
echo "Total number of lines $line_count"

for ((l=0;l<$line_count;l++)); do
    echo "Counter value is $l"             ### In which line are we?
    echo "Field = ${lines[l]}"             ### kepth only to help understanding.
    k="arr$l"                              ### Build the variable arr$COUNTER
    IFS=" " read -ra $k <<<"${lines[l]}"   ### Split into an array a line.
    eval max=\${#$k[@]}                    ### How many elements arr$COUNTER has?
    #echo "field $field and k=$k max=$max" ### Un-quote to "see" inside.
    for ((j=0;j<$max;j++)); do             ### for each element in the line.
        i="$k[$j]"; echo "$i = ${!i}"      ### echo it's value.
    done
done
echo "The End"
echo

However, still, AWK may be faster, if we could execute what you need in AWK.

A similar processing could be done in awk. Assuming the 6 values will be used as an IP (4 of them) and the other two are a number and an epoch time.

Just a very simple sample of an AWK script:

#!/bin/sh
valfile="VALUES_FILE.txt"
awk '
NF==6 { printf ( "IP: %s.%s.%s.%s\t",$1,$2,$3,$4)
        printf ( "number: %s\t",$5+2)
        printf ( "epoch: %s\t",$6)
        printf ( "\n" )
    }
' "$valfile"

Just make a new question with the details.

Bash + using printf in order to print in special format

Using parameter expansion to replace spaces resulting from %-s by dots:

#!/bin/bash
list=(localhost google.com nowhere)
C=1
for M in "${list[@]}"
do
    machine_indented=$(printf '%-20s' "$M")
    machine_indented=${machine_indented// /.}

    if ping -q -c 1  "$M" &>/dev/null ;  then
        printf "(%2d) %s CONNECTION OK\n" "$C" "$machine_indented"
    else
        printf "(%2d) %s CONNECTION FAIL\n" "$C" "$machine_indented"
    fi
    ((C=C+1))
done

Best Answer

Related Solutions

Bash Arrays – Using Variables in Array Names

Bash + using printf in order to print in special format

Related Question