使用Shell脚本根据匹配值更新文件列的需求及代码问题

First, let's break down what's not working in your original script:

• Incorrect variable assignment: Lines like var1 =$18 are invalid—you can't have spaces around =, and $18 doesn't refer to the first column of the current line. To extract columns from a line, you should split the line into variables when reading it (e.g., read col1 col2 col3 <<< "$line").
• Inefficient nested loops: Reading file B every time you process a line from file A is slow and unnecessary.
• Wrong command usage: The mv command moves files—this isn't how you modify the content of lines to build a new file.
• Syntax errors in conditionals: [$var1==$var3] is missing spaces around [ and ], and in ksh, you should use = instead of == for string comparison (or use [[ ]] for safer checks).

Best Solution: Use AWK (Efficient & Clean) #

AWK is designed exactly for this kind of text processing task. Here's a script that will generate your desired file C:

cd /test/files
awk '
    # Process file B (cde.dat) first: store its first two columns as a key, third as value
    NR == FNR {
        map[$1,$2] = $3
        next
    }
    # Now process file A (abc.dat)
    {
        # Check if the first two columns exist in our map
        if (($1,$2) in map) {
            print $1, $2, map[$1,$2]
        } else {
            print $0  # Keep original line if no match
        }
    }
' cde.dat abc.dat > fileC.dat

How This Works: #

• NR == FNR: This condition is true only when we're reading the first input file (cde.dat). We use a 2-dimensional array map to store the third column value, indexed by the first two columns combined.
• For each line in abc.dat, we check if the first two columns exist as a key in map. If yes, we print the first two columns plus the value from map; if not, we print the original line.
• The output is redirected to fileC.dat (your desired file C).

Alternative: Pure KSH Script #

If you need to stick to ksh (note: this requires ksh93 or newer for associative arrays), here's a working version:

cd /test/files

# Create an associative array to store data from file B
typeset -A b_data

# Populate the array with file B's content: key = "col1 col2", value = col3
while read col1 col2 col3; do
    b_data["$col1 $col2"]="$col3"
done < cde.dat

# Process file A to build file C
while read col1 col2 col3; do
    key="$col1 $col2"
    # Check if the key exists in our array
    if [[ -n "${b_data[$key]}" ]]; then
        echo "$col1 $col2 ${b_data[$key]}"
    else
        echo "$col1 $col2 $col3"
    fi
done < abc.dat > fileC.dat

How This Works: #

• We first read all lines from cde.dat into an associative array where each key is the first two columns (joined by a space) and the value is the third column.
• We then iterate over each line in abc.dat, check if the key exists in the array, and print either the modified line (with file B's third column) or the original line.

Both scripts will produce your desired file C:

111 Apple Blue
112 Orange Black
113 Mango Yellow

内容的提问来源于stack exchange，提问作者ganesh_patil