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使用 awk 和 sed 将空白值替换为之前的第一列值

tag-icon • tag-icon text-processing awk sed
使用 awk 和 sed 将空白值替换为之前的第一列值 
john    math
        science
paul    math
        science
rosy    math
jill    science
rob     math
        science
hary    math

期望的输出：

john    math
john    science
paul    math
paul    science
rosy    math
jill    science
rob     math
rob     science
hary    math

答案1

使用awk, 通过作用于多个字段

$ awk 'NF==1{print p "\t" $1; next} {p=$1} 1' ip.txt
john    math
john    science
paul    math
paul    science
rosy    math
jill    science
rob     math
rob     science
hary    math
  • {p=$1} 1对于单个字段以外的行，保存第一列并打印该行
  • NF==1{print p "\t" $1; next}如果仅存在一个字段，则打印上一个字段tab以及输入行中的字段。next将跳过其余语句并处理下一行


如果tab分离不起作用，请使用column

$ awk 'NF==1{print p,$1; next} {p=$1} 1' ip.txt | column -t
john  math
john  science
paul  math
paul  science
rosy  math
jill  science
rob   math
rob   science
hary  math

答案2

你可以用这种方式做到sed这一点：

sed ':n; N; s/\n[^ ]/&/; tsplit; s/^\([^ ]* *\)\([^ ]*\n\) *\([^ ]*\)$/\1\2\1\3/; :split; h; s/\n.*$//; p; g; s/^.*\n//; bn' test.txt

解释

sed '# Start label for loop
:n
# Read next string to main buffer, separated by "\n"
N
# Split and print first string if second starts with non-space character
s/\n[^ ]/&/
tsplit
# "^\([^ ]* *\)" -- First word with spaces, \1.
# "\([^ ]*\n\)"  -- Second word, \2.
# " *"           -- Spaces in second line, throw them.
# "\([^ ]*\\)"   -- Second word in second line, \3.
s/^\([^ ]* *\)\([^ ]*\n\) *\([^ ]*\)$/\1\2\1\3/
# Splitting
:split
# Send both lines to hold buffer
h
# Delete second line, print first
s/\n.*$//
p
# Lines to main buffer, delete first.
g
s/^.*\n//
# Now second file is first, start loop again.
bn' test.txt

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