[shell] awk学习

　　awk处理最后一行

awk '{if(NR>1)print a;a=$0}END{print a="b"}' file
awk 'BEGIN{getline a}{print a;a=$0}END{print a="b"}' file

　　awk域匹配

echo "12 34" | awk '$1 ~ /1/'
echo "12 34" | awk '$1 ~ "1"'
如果把域放后面，记得字符串多的放~前面
echo "12 34" | awk '"123" ~ $1'
echo "12 34" | awk '"1" ~ $1'    #没结果

　　打印九九乘法法

awk 'BEGIN{for(n=1;n<=9;n++){for(i=1;i<=n;i++){printf i"x"n"="i*n" "}print}}'
每行后面多了一个空格
awk 'BEGIN{for(n=1;n<=9;n++){for(i=1;i<=n;i++){end=i==n?"\n":" ";printf i"x"n"="i*n end}}}'

　　求最大值、最小值

awk 'max<$1{max=$1}END{print max}' file
awk '{min=(min=="" || min>$1)?$1:min}END{print min}' file

　　头尾不变，中间行改动

awk '{a[NR]=$0}END{print a[1];for(i=2;i<NR;i++){print a[i]"a"}print a[i]}' file
awk '{a[NR]=$0}END{for(i=1;i<=NR;i++){if(i==1||i==length(a))print a[i];else print a[i]"a"}}' file
sed '1n;$n;s/$/a/' file
awk 'NR==1{print;next}{if(a)print a;a=$0"a"}END{print $0}' file
awk -vn=`grep -c . file` 'NR!=1&&NR!=n{$0=$0"a"}1' file

　　

[root@66a awk]# cat file
"a":"1","b":"2","c":"3","d":"4","e":"5"
"a":"1","b":"2","d":"4"
"c":"3","e":"5"
[root@66a awk]# awk -f what.sh file
abcde
12345
12#4#
##3#5
[root@66a awk]# cat what.sh
BEGIN{FS="[:,]"}
{gsub(/"/,"")}
NR==1{
    for(i=1;i<=NF;i+=2){printf $i;a[++n]=$i};
    print ""
}
{
    for(i=1;i<=NF;i+=2)b[$i]=$(i+1);
    for(i=1;i<=n;i++){
        if(a[i] in b)printf b[a[i]];
        else printf "#"}
    print "";
    delete b
}

　　

[root@66a awk]# cat a1
1 21
3 22
5 12
[root@66a awk]# cat a2
3 27
5 32
[root@66a awk]# cat a3
1 23
5 12
[root@66a awk]# awk -f what.sh a*
id    a1    a2    a3
1    21    0    23
3    22    27    0
5    12    32    12
[root@66a awk]# cat what1.sh
{
    a[$1","FILENAME]=$2;
    b[$1];
}
END{
    printf "id";
    for(i=1;i<ARGC;i++)printf "\t"ARGV[i];
    print "";
    c=asorti(b);
    for(i=1;i<=c;i++){
        s=b[i];
        for(j=1;j<ARGC;j++){
            s=a[b[i]","ARGV[j]]?s"\t"a[b[i]","ARGV[j]]:s"\t0"
        }
        print s;
    }
}

[root@66a awk]# cat what2.sh
ARGV[1]==FILENAME{c[++n]=$1}
{ a[$1","FILENAME]=$2 }
END {
    printf "id";
    for(i=1;i<ARGC;i++)printf "\t"ARGV[i];
    print "";
    for (i=1;i<=n;i++) {
        s=c[i];
        for (j=1;j<ARGC;j++){
            if(c[i]","ARGV[j] in a)s=s"\t"a[c[i]","ARGV[j]];
            else s=s"\t0";
        }
        print s;
    }
}