在awk和bash脚本中转义

Question

I'm trying to change the numbers in column 2, 3, and 4 of the files. To do that, I have following script

for i in 0.8 0.9 1 1.1 1.2; do
original=10.9398135077
fraction=`bc <<< "$i*$original"`
convert=0.529177
awk '{printf "%-2s %10.5f %10.5f %10.5f\n", $1, ($2*"\$fraction"*"\$convert"), ($3*"\$fraction"*"\$convert"), ($4*"\$fraction"*"\$convert")}' temp2_${i}.txt > coord_${i}.txt
done

and my temp2_0.8.txt looks like following:

Cu      -0.000000000   0.000000000  -0.000000000
Cu       0.500000000  -0.000000000   0.500000000
Cu       0.000000000   0.500000000   0.500000000
Cu       0.500000000   0.500000000   0.000000000
S        0.398420013   0.398420013   0.398420013
S        0.898420013   0.398420013   0.101579987
S        0.398420013   0.101579987   0.898420013
S        0.101579987   0.898420013   0.398420013
S        0.601579987   0.601579987   0.601579987
S        0.898420013   0.101579987   0.601579987
S        0.101579987   0.601579987   0.898420013
S        0.601579987   0.898420013   0.101579987

But if I execute my script, I get this message:

awk: warning: escape sequence `\$' treated as plain `$'

And I get 0.00000 in all of my converted files. It seems I failed to escape keywords in the awk.... how can I multiply "fraction" and "convert" to the column number 2, 3, and 4 with awk properly?

Add:) I used \\$fraction instead of "\\$fraction" but it gives me error "backslash not last character on line"

Answer 1

Inside single quotes, the shell ignores dollars, backslashes, double quotes, back-ticks — only single quotes are interesting. The awk script therefore gets the values wrong. Use -v variable="$value" to pass shell variables to the script. Why bother with bc ? awk can multiply quite happily.

original=10.9398135077
convert=0.529177
for i in 0.8 0.9 1 1.1 1.2
do
    awk -v org="$original" -v factor="$i" -v conv="$convert" \
        'BEGIN { multiplier = factor * original * convert }
         { printf "%-2s %10.5f %10.5f %10.5f\n", $1,
                  ($2 * multiplier),
                  ($3 * multiplier),
                  ($4 * multiplier) }' temp2_${i}.txt > coord_${i}.txt
done

Answer 2

You don't need a shell loop for this:

awk '
BEGIN {
    original = 10.9398135077
    convert = 0.529177
    split("0.8 0.9 1 1.1 1.2", factors)
    for (i in factors) {
        ARGV[i] = "temp2_"i".txt"
        outfiles[i] = "coord_"i".txt"
        multipliers[i] = factors[i] * original * convert
        ARGC++
    }
}
{
    printf "%-2s %10.5f %10.5f %10.5f\n", $1,
        $2 * multipliers[ARGIND],
        $3 * multipliers[ARGIND],
        $4 * multipliers[ARGIND] > outfiles[ARGIND]
}
'

If you aren't using GNU awk then add a FNR==1{ARGIND++} statement after the BEGIN{...} section.