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1.1 ! root 1: ! 2: ! 3: eval Command eval ! 4: ! 5: ! 6: ! 7: ! 8: Evaluate arguments ! 9: ! 10: eevvaall [_t_o_k_e_n ...] ! 11: ! 12: The shell sh normally evaluates each token of an input line ! 13: before executing it. During evaluation, the shell performs ! 14: parameter, command, and file name pattern substitution, as ! 15: described in sh. The shell does not interpret special characters ! 16: after performing substitution. ! 17: ! 18: eval is useful when an additional level of evaluation is re- ! 19: quired. eval evaluates its arguments and treats the result as ! 20: shell input. For example, ! 21: ! 22: ! 23: A='>file' ! 24: echo a b c $A ! 25: ! 26: ! 27: simply prints the output ! 28: ! 29: ! 30: a b c >file ! 31: ! 32: ! 33: because `>' has no special meaning after substitution, but ! 34: ! 35: ! 36: A='>file' ! 37: eval echo a b c $A ! 38: ! 39: ! 40: redirects the output ! 41: ! 42: ! 43: a b c ! 44: ! 45: ! 46: to file. Similarly, ! 47: ! 48: ! 49: A='$B' ! 50: B='string' ! 51: echo $A ! 52: eval echo $A ! 53: ! 54: ! 55: prints ! 56: ! 57: ! 58: ! 59: ! 60: ! 61: ! 62: ! 63: ! 64: COHERENT Lexicon Page 1 ! 65: ! 66: ! 67: ! 68: ! 69: eval Command eval ! 70: ! 71: ! 72: ! 73: $B ! 74: string ! 75: ! 76: ! 77: In the first echo the shell performs substitution only once. ! 78: ! 79: The shell executes eval directly. ! 80: ! 81: ***** See Also ***** ! 82: ! 83: commands, sh ! 84: ! 85: ! 86: ! 87: ! 88: ! 89: ! 90: ! 91: ! 92: ! 93: ! 94: ! 95: ! 96: ! 97: ! 98: ! 99: ! 100: ! 101: ! 102: ! 103: ! 104: ! 105: ! 106: ! 107: ! 108: ! 109: ! 110: ! 111: ! 112: ! 113: ! 114: ! 115: ! 116: ! 117: ! 118: ! 119: ! 120: ! 121: ! 122: ! 123: ! 124: ! 125: ! 126: ! 127: ! 128: ! 129: ! 130: COHERENT Lexicon Page 2 ! 131: ! 132:
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